Ans:- JavaScript is a programming language that is primarily used to create interactive front-end web applications. It is a client-side scripting language, which means that the code is executed on the user's device (in the web browser) rather than on a server. JavaScript is used to create things like interactive forms, dynamic content, and interactive maps on websites, and it also allows for creating browser-based games. It can also be run on servers using Node.js.
Q) How is JavaScript different from other programming languages?
Ans:- JavaScript is a scripting language, which means it is mainly used for small programs and scripts that are executed at runtime. It is different from other programming languages such as Java, C++, and Python, which are considered to be general-purpose programming languages and can be used to build a wide range of applications such as desktop software, mobile apps, and servers.
JavaScript is mainly used to create interactive front-end web applications, which run in the browser. This means that the code is executed on the user's device, rather than on a server, which is different from server-side languages such as PHP and Ruby.
JavaScript is also different from other programming languages in that it is an interpreted language, which means that the code is executed directly by the browser, rather than being compiled into machine code first. This allows for faster development and testing, but can also result in slower performance.
Overall, JavaScript is known for its versatility and ability to be used on the front-end and back-end of web development, making it a popular choice for web developers.
Q) What are the data types in JavaScript?
Ans:-JavaScript has six basic data types:
Number: This data type is used to represent numeric values, such as integers and floating-point numbers.
String: This data type is used to represent text values, such as "hello world" or "John Doe".
Boolean: This data type is used to represent true or false values.
Symbol: This data type is used to create unique identifiers.
Undefined: This data type represents a value that has not been assigned to a variable.
Object: This data type is used to represent collections of data, such as arrays and key-value pairs.
Additionally, in JavaScript there is also a special data type called "null" which can be assigned to a variable to indicate that it has no value.
JavaScript is a loosely typed language, which means that variables do not have to be explicitly declared with a data type, and their type can change dynamically during runtime.
Q) How do you declare a variable in JavaScript?
Ans:- You can declare a variable in JavaScript using the **var**
, **let**
, or **const**
keyword. For example: **var x;**
, **let y;**
, **const z;**
. You can also assign a value to a variable at the same time you declare it, like **var x = 5;**
, **let y = "hello";**
, **const z = true;**
.
Q) What is hoisting in JavaScript?
Hoisting is a behavior in JavaScript where variable and function declarations are moved to the top of their scope. This means that variable and function declarations are accessible before the code that declares them is executed. In practice, this means that variable declarations are automatically moved to the top of their scope, and variable assignments stay in their original place.
Q) What is closure in JavaScript?
Ans:- A closure is a function that has access to variables in its parent scope, even after the parent function has returned. Closures are created when a function is defined inside of another function, and they allow the inner function to "remember" the variables in the outer function's scope. Closures are often used in JavaScript to create "private" variables and methods.
Q) What is the difference between let and var in JavaScript?
Ans:- The main difference between the **let**
and **var**
keywords is the scope in which a variable is declared. Variables declared with **var**
have function scope, which means they are accessible within the entire function in which they are declared, as well as any nested functions. Variables declared with **let**
and **const**
have block scope, which means they are only accessible within the block in which they are declared, as well as any nested blocks.
Q) What is the difference between == and === in JavaScript?
Ans:- The **==**
operator in JavaScript is used to compare values for equality, but it does type coercion, meaning it converts the operands to the same type before making the comparison. The **===**
operator, also called the strict equality operator, also compares values for equality but it doesn't do type coercion, so the operands must be of the same type. It's recommended to use **===**
as it's more precise and less prone to bugs caused by type coercion.
Q) What is the difference between null and undefined in JavaScript?
**Ans:- ** **undefined**
is a special value in JavaScript that indicates that a variable has been declared but has not been assigned a value. **null**
is a value that can be assigned to a variable to indicate that it has no value. In other words, **undefined**
is a value that a variable has when it has been declared but not initialized, while **null**
is a value that can be assigned to indicate that a variable has no value.
Q) What is the difference between a for loop and a forEach loop in JavaScript?
Ans:- A **for**
loop is a control structure used to iterate over an array or an object and execute a block of code for each element. It uses a counter variable to keep track of the current index and a stopping condition to end the loop. A **forEach**
loop is a method provided by arrays to iterate over its elements, it doesn't use a counter variable and also it doesn't return anything. It's also a more simple and elegant way to iterate over an array.
Q) What is the difference between a while loop and a do-while loop in JavaScript?
Ans:- A **while**
loop is a control structure that repeatedly runs a block of code as long as a specified condition is true. The loop will not execute if the condition is false when it is first encountered. A **do-while**
loop is similar to a **while**
loop, but it will always run the code block at least once, and then it will check the condition to determine if it should continue running.
Q) What is the difference between a function expression and a function declaration in JavaScript?
Ans:- A function expression is when a function is assigned to a variable, like **const add = function(a, b) { return a + b; }**
A function declaration is when a function is defined by using the **function**
keyword, like **function add(a, b) { return a + b; }**
The main difference between the two is that function expressions are not hoisted, which means they cannot be called before they are defined, while function declarations are hoisted and can be called before they are defined. Function expressions are also called anonymous functions, because they don't have a name, unless you assign them to a variable.
Q) What is the difference between an object and an array in JavaScript?
Ans:- An object is a collection of key-value pairs, where each key is a string and each value can be of any data type. An object can be used to store data in a structured way and can be accessed using dot notation or bracket notation. An array is an ordered collection of elements, where each element can be of any data type and can be accessed using an index. Arrays are zero-indexed, meaning the first element is at index 0, the second element is at index 1, and so on.
Q) How do you create an object in JavaScript?
Ans:- There are several ways to create an object in JavaScript:
**const myObj = { key1: value1, key2: value2 }**
**const myObj = new Object()**
**const myObj = Object.create(null)**
Q) How do you create an array in JavaScript?
Ans:- There are several ways to create an array in JavaScript:
**const myArray = [element1, element2, element3]**
**const myArray = new Array()**
**const myArray = Array.of(element1, element2, element3)**
Q) How do you add elements to an array in JavaScript?
Ans:- There are several ways to add elements to an array in JavaScript:
**myArray.push(element)**
**myArray.unshift(element)**
**myArray.splice(index, 0, element)**
**myArray[myArray.length] = element**
It's worth noting that the Array.push() method adds an element to the end of an array, while the Array.unshift() method adds an element to the beginning of an array. The splice() method allows you to insert an element at a specific index in the array and can also be used to remove elements from an array.
Q) How do you remove elements from an array in JavaScript?
Ans:- There are several ways to remove elements from an array in JavaScript:
**myArray.pop()**
remove the last element of the array.**myArray.shift()**
remove the first element of the array.**myArray.splice(index, 1)**
remove an element from a specific index.**myArray = myArray.filter(element => element !== value)**
remove all elements that match a certain condition.Q) How do you iterate over an array in JavaScript?
Ans:- There are several ways to iterate over an array in JavaScript:
Q) How do you sort an array in JavaScript?
Ans:- The Array.sort() method can be used to sort an array in JavaScript. By default, it sorts the elements in ascending order. The sort method sorts the elements of an array in place and returns the sorted array.myArray.``sort``();
You can also pass a function as an argument to sort method to sort the elements based on a specific condition.
Q) How do you reverse an array in JavaScript?
Ans:- The Array.reverse() method can be used to reverse an array in JavaScript. It modifies the array in place and returns the reversed array.
You can also use a combination of sort method and reverse method to sort the array in descending order.
You can also use the **slice()**
method and **concat()**
to reverse an array.
Or use the spread operator to reverse an array
It's worth noting that these methods return a new array, leaving the original array unchanged.
Q) How do you filter an array in JavaScript?
Ans:- The Array.filter() method can be used to filter an array in JavaScript. It takes a callback function as an argument, which is called for each element in the array. If the function returns true, the element is included in the new filtered array, otherwise, it is not.
Q) How do you map an array in JavaScript?
Ans:- The Array.map() method can be used to create a new array with the same length, but with each element transformed according to a provided function.
Q) How do you reduce an array in JavaScript?
Ans:- The Array.reduce() method can be used to reduce an array to a single value. It takes a callback function as an argument, which is called for each element in the array, and it accumulates the result of the function, the final result is returned.
Q) How do you concatenate two arrays in JavaScript?
Ans:- There are several ways to concatenate two arrays in JavaScript:
It's worth noting that the first two methods return a new array, leaving the original arrays unchanged, while the last method modifies the first array in place. It's also important to note that if you want to concatenate more than two arrays you can chain the concat() method or use the spread operator multiple times.
Q) What is the difference between .forEach() and .map() in JavaScript?
Ans:- **.forEach()**
method is used to iterate over an array and perform a specific action on each element of the array, without changing the original array. It doesn't return a new array, it only performs the action on each element.
**.map()**
method is used to iterate over an array, perform a specific action on each element and return a new array containing the results of the action on each element. This method does not change the original array.
Q) What is the difference between .filter() and .find() in JavaScript?
Ans:- **.filter()**
method is used to filter an array based on a condition, it creates a new array with all the elements that pass the test implemented by the provided function. It returns all the elements that match the condition.
**.find()**
method is used to return the value of the first element in an array that pass a test implemented by the provided function. It returns only the first element that match the condition.
Q) What is the difference between .reduce() and .reduceRight() in JavaScript?
Ans:- **.reduce()**
method applies a function to each element in an array and reduces it to a single value. It starts the iteration from the leftmost element and goes to the right.
**.reduceRight()**
method is similar to .reduce() method but it starts the iteration from the rightmost element and goes to the left.
Q) What is the difference between .slice() and .splice() in JavaScript?
Ans:- **.slice()**
method returns a shallow copy of a portion of an array into a new array object selected from begin to end (end not included) where begin and end represent the index of items in that array. The original array will not be modified.
**.splice()**
method changes the contents of an array by removing or replacing existing elements and/or adding new elements in place. It modifies the original array. It can be used to add, remove and replace elements in an array.
Both methods are used to manipulate arrays but they have different purposes and return different results.
Q) What is the difference between .sort() and .reverse() in JavaScript?
Ans:- **.sort()**
method is used to sort the elements of an array in place and returns the sorted array. It sorts the elements of an array according to the string Unicode code points of elements.
**.reverse()**
method is used to reverse the order of the elements of an array in place and returns the reversed array.
Q) How do you create a class in JavaScript?
Ans:- JavaScript classes were introduced in ECMAScript 6 (ES6) and can be defined using the **class**
keyword.
Q) How do you create an object from a class in JavaScript?
Ans:- JavaScript classes are used to create objects using the **new**
keyword.
Q) How do you inherit from a class in JavaScript?
Ans:- JavaScript classes can inherit from other classes using the **extends**
keyword.
This allows the ChildClass to inherit the methods and properties of ParentClass, and also add its own methods and properties. It's worth noting that the **super()**
call in the constructor is used to call the parent class' constructor and pass it the necessary parameters.
Q) How do you create a constructor in JavaScript?
Ans:- In JavaScript, a constructor is a special method that gets called when an object is created from a class. It is defined using the **constructor**
keyword and it can accept parameters.
Q) How do you add methods to a class in JavaScript?
Ans:- Methods can be added to a class by defining them inside the class. Methods defined inside a class are usually called instance methods because they are available to objects created from the class.
Q) How do you add properties to a class in JavaScript?
Ans:- Properties can be added to a class by defining them inside the constructor or by defining them outside the class and adding them to the class prototype. Properties defined inside a class are usually called instance properties because they are unique to each object created from the class.
Q) What is the difference between a prototype and a class in JavaScript?
Ans:- A class is a blueprint for creating objects (instances), it's a way to create a new object type with its own methods and properties. It's a way to define a structure for an object.
A prototype is the object that is used as a template for creating new objects. It's an object that is automatically associated with a class and it's used to define the properties and methods that will be available to all instances of the class. It's a way to define the behavior of an object.
All objects created from a class have the same prototype. Any changes made to the prototype will be reflected in all instances of the class.
In summary, a class defines the structure of an object and a prototype defines the behavior of an object.
Q) What is the difference between call and apply in JavaScript?
Ans:- Both **call**
and **apply**
are used to call a function and set the **this**
value within the function. The difference is in the way they accept the arguments:
**call**
method accepts an argument list, where each argument is passed in separately.**apply**
method accepts a single array-like object, where all the arguments are passed as an array.Q) What is the difference between bind and call in JavaScript?
Ans:- Both **bind**
and **call**
are used to call a function and set the **this**
value within the function. The difference is in their return values:
**bind**
method returns a new function with the **this**
value bound to the first argument passed to it. It doesn't call the function immediately.**call**
method calls the function immediately with the **this**
value set to the first argument passed to it.Q) What is the difference between a promise and a callback in JavaScript?
Ans:- A promise is an object that represents the eventual completion (or failure) of an asynchronous operation, and its resulting value. It allows you to register callbacks for when the promise is fulfilled (resolved) or rejected.
A callback is a function passed to another function as an argument, that gets executed after the first function is done. It's a way to handle the result of an asynchronous operation.
Promise is a higher-level abstraction built on top of callbacks, it provides a more convenient and flexible way to handle the results of asynchronous operations.
Q) How do you create a promise in JavaScript?
Ans:- Promises can be created using the **Promise**
constructor, which takes a single function as an argument. The function is passed two arguments, **resolve**
and **reject**
, which can be used to signal the completion (or failure) of the asynchronous operation.
Q) How do you handle a promise in JavaScript?
Ans:- Promises can be handled using the **then**
and **catch**
methods. The **then**
method is called when the promise is resolved, and it takes a single function as an argument, which is passed the result of the promise. The **catch**
method is called when the promise is rejected, and it takes a single function as an argument, which is passed the error.
Q) How do you chain promises in JavaScript?
Ans:- Promises can be chained using the **then**
method. Each **then**
method returns a new promise, which can be used to call the next **then**
method.
Q) How do you handle errors in a promise in JavaScript?
Ans:- Errors can be handled using the **catch**
method, which is called when the promise is rejected. It takes a single function as an argument, which is passed the error.
Q) What is async/await in JavaScript?
Ans:- **async/await**
is a way to handle promises in a more synchronous style. The **async**
keyword is used to create an asynchronous function, and the **await**
keyword is used to wait for a promise to be resolved.
Q) How do you use async/await in JavaScript?
Ans:- To use **async/await**
, you need to define an asynchronous function using the **async**
keyword, and then use the **await**
keyword to wait for a promise to be resolved.
Q) How do you handle errors with async/await in JavaScript?
Ans:- Errors can be handled using a **try/catch**
block within the asynchronous function.
Q) How do you use fetch in JavaScript?
Ans:- The **fetch()**
method can be used to make HTTP requests in JavaScript. It returns a promise that resolves to the response of the request.
Q) How do you handle errors with fetch in JavaScript?
Ans:- Errors can be handled by adding a **catch**
method to the promise chain
Q) How do you make an HTTP request in JavaScript?
Ans:- You can use the **fetch()**
method, the **XMLHttpRequest()**
object, or a library like **axios**
or **superagent**
to make an HTTP request in JavaScript.
Q) How do you handle errors with an HTTP request in JavaScript?
Ans:- Errors can be handled by adding an error handling function or a **catch**
method to the promise chain.
It's worth noting that handling errors can vary depending on the method or library used to make the request.
Overall, handling errors is an important aspect of making HTTP requests in JavaScript, it is a good practice to check the status of the response and handle any errors that may have occurred during the request.
Q) What is an event in JavaScript?
Ans:- In JavaScript, an event is an action or occurrence, such as a user clicking on a button, a page finishing loading, or an element being updated, that can be detected by your script. Events can be triggered by the user, the browser, or the system, and can be handled by JavaScript code to create interactive and dynamic web pages.
Q) How do you create an event in JavaScript?
Ans:- JavaScript events can be created by the browser, the user, or by the script itself. For example, a user clicking on a button generates a click event, a page finishing loading generates a load event, and a script can create a custom event using the **new Event()**
constructor or **Event()**
function.
Q) How do you handle an event in JavaScript?
Ans:- JavaScript events can be handled using event listeners. An event listener is a function that is registered to listen for a specific event on a particular element. The event listener is executed when the event occurs.
Q) How do you prevent the default behavior of an event in JavaScript?
Ans:- The default behavior of an event can be prevented by calling the **preventDefault()**
method on the event object passed to the event listener.
Q) What is event bubbling and event capturing in JavaScript?
Ans:- In JavaScript, events are propagated in two phases: event capturing and event bubbling.
Event capturing is the phase in which the event starts at the window object and propagates down the DOM tree to the target element.
Event bubbling is the phase in which the event propagates back up the DOM tree from the target element to the window object.
It's worth noting that by default, most DOM events propagate using event bubbling, but you can use the **useCapture**
parameter in the addEventListener() method to specify event capturing.
Event capturing is less commonly used, but it can be useful in some cases, such as when you want to handle an event on a parent element before it reaches the target element.
Q) What is the difference between addEventListener and attachEvent in JavaScript?
Ans:- **addEventListener**
is the standard method for adding event listeners to elements in modern web browsers (like Chrome, Firefox, etc.). It allows you to add multiple listeners for the same event on the same element, and it supports event capturing and bubbling.
**attachEvent**
is a Microsoft proprietary method for adding event listeners to elements that was used in older versions of Internet Explorer. It only supports event bubbling and only allows one listener per event per element.
Q) What is the difference between preventDefault and stopPropagation in JavaScript?
Ans:- **preventDefault()**
is used to prevent the default behavior of an event from occurring. For example, it can be used to prevent a link from navigating to a new page or a form from submitting.
**stopPropagation()**
is used to prevent the event from propagating further up or down the DOM tree. For example, it can be used to prevent an event from reaching parent or child elements.
Q) What is the difference between global and window in JavaScript?
Ans:- In a web browser, **window**
is the global object, and all global variables and functions are properties and methods of the **window**
object.
In a Node.js environment, **global**
is the global object, and all global variables and functions are properties and methods of the **global**
object.
In both cases, the **global**
or **window**
object provides a way to access global variables and functions from anywhere in the code.
Q) What is the difference between let and const in JavaScript?
Ans:- **let**
is used to declare a variable, and the variable can be reassigned a new value at any time.
**const**
is used to declare a variable that cannot be reassigned a new value after it's been declared. It is used for variables that should not change after they are set.
Q) What is the difference between Object.freeze and Object.seal in JavaScript?
Ans:- **Object.freeze**
is a method that makes an object immutable. It prevents new properties from being added to the object, existing properties from being removed, and prevents the modification of property attributes.
**Object.seal**
is a method that makes an object non-extensible, it prevents new properties from being added to the object, but existing properties can still be modified.
Q) What is the difference between Object.create and new in JavaScript?
Ans:- **Object.create**
is a method that creates a new object with the specified prototype object and properties.
**new**
is an operator used to create an instance of an object based on a constructor function. It creates a new object with the specified prototype and properties.
Q) What is the difference between Object.assign and Object.merge in JavaScript?
Ans:- **Object.assign**
is a method that copies the values of all enumerable own properties from one or more source objects to a target object.
What is the difference between Array.forEach and Array.map in JavaScript? What is the difference between Array.filter and Array.find in JavaScript? What is the difference between Array.reduce and Array.reduceRight in JavaScript? What is the difference between Array.slice and Array.splice in JavaScript?
Q) What is the difference between Array.forEach and Array.map in JavaScript?
Ans:- **Array.forEach**
is a method that applies a provided function to each element of an array. It does not return a new array and it's mainly used for side-effects.
**Array.map**
is a method that creates a new array with the results of calling a provided function on every element in the calling array. The new array will have the same length as the original array and the returned array will have the same order as the original array.
Q) What is the difference between Array.filter and Array.find in JavaScript?
Ans:- **Array.filter**
is a method that creates a new array with all elements that pass the test implemented by the provided function. It returns a new array that contains all elements that pass the test.
**Array.find**
is a method that returns the value of the first element in the array that satisfies the provided testing function. Otherwise undefined is returned.
Q) What is the difference between Array.reduce and Array.reduceRight in JavaScript?
Ans:- **Array.reduce**
is a method that applies a function against an accumulator and each element in the array (from left to right) to reduce it to a single value.
**Array.reduceRight**
is the same as Array.reduce but it applies the function against an accumulator and each element in the array (from right to left) to reduce it to a single value.
Q) What is the difference between Array.slice and Array.splice in JavaScript?
Ans:- **Array.slice**
is a method that returns a shallow copy of a portion of an array into a new array object selected from begin to end (end not included). The original array will not be modified.
What is the difference between Array.sort and Array.reverse in JavaScript? What is the difference between String.slice and String.substring in JavaScript? What is the difference between String.split and String.replace in JavaScript? What is the difference between String.concat and String.join in JavaScript? What is the difference between String.trim and String.trimStart in JavaScript?
Q) What is the difference between Array.sort and Array.reverse in JavaScript?
Ans:- **Array.sort**
is a method that sorts the elements of an array in place and returns the sorted array. The default sort order is built upon converting the elements into strings, then comparing their sequences of UTF-16 code units values.
**Array.reverse**
is a method that reverses the order of the elements in an array in place and returns the reversed array.
Q) What is the difference between String.slice and String.substring in JavaScript?
Ans:- **String.slice**
is a method that extracts a section of a string and returns a new string. It takes two arguments, the starting index and the ending index (not included) and it can take negative values.
**String.substring**
is a method that returns the characters in a string between two indexes into the string. It also takes two arguments, the starting index and the ending index (not included) and it can't take negative values.
Q) What is the difference between String.split and String.replace in JavaScript?
Ans:- **String.split**
is a method that splits a string into an array of substrings. It takes one argument, the separator to use when splitting the string.
**String.replace**
is a method that replaces the first or all occurrences of a specified value with another value. It takes two arguments, the value to be replaced and the value to replace it with.
Q) What is the difference between String.concat and String.join in JavaScript?
Ans:- **String.concat**
is a method that combines the text of two or more strings and returns a new string.
**String.join**
is a method that joins all elements of
an array into a string, and returns the string. It takes one argument, the separator to use when joining the elements of the array.
Q) What is the difference between String.trim and String.trimStart in JavaScript?
Ans:- **String.trim**
is a method that removes whitespace from both ends of a string. It removes spaces, tabs, and newlines from the beginning and end of the string.
**String.trimStart**
is a method that removes whitespace from the beginning of a string. It removes spaces, tabs, and newlines from the beginning of the string.
**String.trimEnd()**
is similar to **String.trimStart()**
and it removes whitespace from the end of a string.
Q) What is the difference between String.trimEnd and String.trimLeft in JavaScript?
Ans:- **String.trimEnd**
is a method that removes whitespace from the end of a string. It removes spaces, tabs, and newlines from the end of the string.
**String.trimLeft**
(or **String.trimStart()**
) is a method that removes whitespace from the beginning of a string. It removes spaces, tabs, and newlines from the beginning of the string.
In summary **String.trimEnd()**
is used to remove whitespace from the end of the string and **String.trimLeft()**
is used to remove whitespace from the start of the string.
Q) What is the difference between String.trimRight and String.toLowerCase in JavaScript?
Ans:- **String.trimRight**
is a method that removes whitespace from the end of a string. It removes spaces, tabs, and newlines from the end of the string.
**String.toLowerCase**
is a method that converts all the characters in a string to lowercase. It does not affect the original string and returns a new string with all the characters in lowercase.
In summary, **String.trimRight()**
is used to remove whitespace from the end of the string and **String.toLowerCase()**
is used to convert all the characters in a string to lowercase.
Q) What is the difference between String.toUpperCase and String.toLocaleLowerCase in JavaScript?
Ans:- **String.toUpperCase**
is a method that converts all the characters in a string to uppercase. It does not affect the original string and returns a new string with all the characters in uppercase.
**String.toLocaleUpperCase**
is a method that converts all the characters in a string to uppercase, taking into account the host environment's current locale. It does not affect the original string and returns a new string with all the characters in uppercase.
The main difference between **String.toUpperCase()**
and **String.toLocaleUpperCase()**
is that **String.toLocaleUpperCase()**
takes into account the host environment's current locale, which might affect the result, while **String.toUpperCase()**
converts all the characters in a string to uppercase using the Unicode standard.
**String.toLowerCase**
is similar to **String.toUpperCase()**
but it converts all the characters in a string to lowercase. **String.toLocaleLowerCase**
is similar to **String.toLocaleUpperCase()**
but it converts all the characters in a string to lowercase, taking into account the host environment's current locale.
Q) What is the difference between a function expression and an arrow function in JavaScript?
Ans:- In JavaScript, there are two ways to define a function: function expressions and arrow functions.
A function expression is a function that is defined and assigned to a variable. The function keyword is used to define the function, followed by the function name (if any) and the function's parameters.
An arrow function is a shorthand syntax for defining a function expression. Instead of using the function keyword, an arrow (**=>**
) is used to define the function. Arrow functions do not have their own **this**
binding, so **this**
refers to the parent scope.
In summary, the main difference between a function expression and an arrow function is the syntax used to define the function. Function expressions use the **function**
keyword, while arrow functions use the **=>**
syntax. Arrow functions also have lexical **this**
binding, meaning **this**
refers to the parent scope.
Additionally, Arrow function expressions are best suited for non-method functions, while Function expressions are best suited for methods, and constructors.
Q) How do you create a template literals in JavaScript?
Ans:- A template literal is a way to create a string that includes expressions and variables.
Q) What is the difference between a for...in loop and a for...of loop in JavaScript?
Ans:- A **for...in**
loop iterates over the enumerable properties of an object. It is often used to iterate over the properties of an object, and not over the elements of an array.
A **for...of**
loop iterates over the values of an iterable object, such as an array. It can be used to iterate over the elements of an array.
Q) What is the difference between a synchronous and an asynchronous function in JavaScript?
Ans:- A synchronous function is a function that runs to completion before moving on to the next line of code. The program execution is blocked until the function completes its execution.
An asynchronous function is a function that runs in the background, allowing the program to continue executing other code while it is running. It uses callback functions, promises, or async/await to signal when it has completed its execution.
Q) What is the difference between a local and a global scope in JavaScript?
Ans:- A local scope is the area of a program where a variable or a function is defined and can only be accessed within that area. A variable or function defined within a function has a local scope that is only accessible within that function.
A global scope is the area of a program where a variable or a function is defined and can be accessed throughout the entire program. A variable or function defined outside of a function has a global scope that is accessible throughout the entire program.
Q) What is a closure and how do you create one in JavaScript?
Ans:- A closure is a function that has access to the variables and functions defined in its parent scope, even after the parent function has returned. A closure is created by returning a function defined inside of another function.
Q) What is a higher-order function in JavaScript and give an example of one?
Ans:- A higher-order function is a function that takes one or more functions as arguments, or returns a function as a result. An example of a higher-order function is **Array.prototype.map()**
, which takes a callback function as an argument and applies it to each element of an array.
In this example, **map()**
is a higher-order function that takes a callback function as an argument and applies it to each element of the array.
What is the difference between the Document Object Model (DOM) and the Browser Object Model (BOM)? How do you access and modify the DOM using JavaScript? How do you create a new element in the DOM using JavaScript? How do you delete an element from the DOM using JavaScript? How do you change the styles of an element in the DOM using JavaScript?
Q) What is the difference between the Document Object Model (DOM) and the Browser Object Model (BOM)?
Ans:- The Document Object Model (DOM) is a programming interface for HTML and XML documents. It represents the structure of a document as a tree of nodes and provides a way to access and modify the content and structure of a document using JavaScript. The DOM is used to manipulate the content, structure and styles of a web page.
The Browser Object Model (BOM) is a programming interface for web browsers. It provides a way to access and manipulate the browser's window and its properties, such as the history, location, and navigator. The BOM is used to manipulate the browser itself, not the content of a web page.
Q) How do you access and modify the DOM using JavaScript?
Ans:- You can access and modify the DOM using JavaScript by using DOM methods and properties. The most common way to access elements in the DOM is by using the **document.getElementById()**
method, which returns a reference to the element with the specified ID.
You can also access elements using other methods such as **document.getElementsByTagName()**
, **document.getElementsByClassName()**
and **document.querySelector()**
.
Once you have a reference to an element, you can use properties and methods to modify its content, attributes, and styles. For example, you can use the **innerHTML**
property to change the content of an element and the **setAttribute()**
method to change the value of an attribute.
Q) How do you create a new element in the DOM using JavaScript?
Ans:- You can create a new element in the DOM using the **document.createElement()**
method. This method takes the tag name of the element you want to create as an argument and returns a reference to the new element. Once you have a reference to the new element, you can set its attributes and content using properties and methods.
Q) How do you delete an element from the DOM using JavaScript?
Ans:- You can delete an element from the DOM using the **remove()**
method or the **removeChild()**
method.
Q) How do you change the styles of an element in the DOM using JavaScript?
Ans:- You can change the styles of an element in the DOM using the **style**
property. This property allows you to access and modify the inline styles of an element.
Q) What is the difference between the Document Object Model (DOM) and the Browser Object Model (BOM)?
Ans:- The Document Object Model (DOM) is a programming interface for HTML and XML documents. It represents the structure of a document as a tree of nodes and provides a way to access and modify the content and structure of a document using JavaScript. The DOM is used to manipulate the content, structure and styles of a web page.
The Browser Object Model (BOM) is a programming interface for web browsers. It provides a way to access and manipulate the browser's window and its properties, such as the history, location, and navigator. The BOM is used to manipulate the browser itself, not the content of a web page.
Q) How do you access and modify the DOM using JavaScript?
Ans:- You can access and modify the DOM using JavaScript by using DOM methods and properties. The most common way to access elements in the DOM is by using the **document.getElementById()**
method, which returns a reference to the element with the specified ID.
You can also access elements using other methods such as **document.getElementsByTagName()**
, **document.getElementsByClassName()**
, **document.querySelector()**
and **document.querySelectorAll()**
.
Once you have a reference to an element, you can use properties and methods to modify its content, attributes, and styles. For example, you can use the **innerHTML**
property to change the content of an element, the **setAttribute()**
method to change the value of an attribute, and the **style**
property to change the styles of an element.
Q) How do you create a new element in the DOM using JavaScript?
Ans:- You can create a new element in the DOM using JavaScript by using the **document.createElement()**
method. This method takes the tag name of the element you want to create as an argument and returns a reference to the new element. Once you have a reference to the new element, you can set its attributes and content using properties and methods, and then use **appendChild()**
or **insertBefore()**
method to insert it into the DOM.
Q90) How do you delete an element from the DOM using JavaScript?
Ans:- You can delete an element from the DOM using the **remove()**
method or the **removeChild()**
method.
Q91) How do you change the styles of an element in the DOM using JavaScript?
Ans:- You can change the styles of an element in the DOM using the **style**
property. This property allows you to access and modify the inline styles of an element.
You can also use classList property to add, remove or toggle class on an element
You can also use className property to add or remove class on an element
Q92) How do you handle events in the DOM using JavaScript?
Ans:- You can handle events in the DOM using JavaScript by using event listeners. An event listener is a function that is executed when a specific event occurs on an element. To attach an event listener to an element, you use the **addEventListener()**
method, which takes the event type and the function to be executed as arguments.
You can also use the **on**
syntax to attach the event
Q93) How do you create a timer in JavaScript?
Ans:- A timer in JavaScript is a way to execute a function after a specific amount of time. There are three ways to create a timer in JavaScript: **setTimeout()**
, **setInterval()**
, and **requestAnimationFrame()**
.
**setTimeout()**
is used to execute a function once after a specific amount of time. It takes two arguments: the function to be executed and the time in milliseconds.
**setInterval()**
is used to execute a function repeatedly at a given interval. It takes two arguments: the function to be executed and the time in milliseconds.
**requestAnimationFrame()**
is used to execute a function before the browser repaints the screen. It is typically used for animations, and it takes a single argument: the function to be executed.
Q94) How do you clear a timer in JavaScript?
Ans:- You can clear a timer in JavaScript by using the **clearTimeout()**
or **clearInterval()**
method. These methods take a single argument: the ID of the timer returned by the **setTimeout()**
or **setInterval()**
method.