What is the difference between Object.freeze and Object.seal in JavaScript?

Table of Contents

• Introduction
• What is Object.freeze?
  • Definition
  • Characteristics
  • Example
• What is Object.seal?
  • Definition
  • Characteristics
  • Example
• Key Differences
• Conclusion

Introduction

In JavaScript, Object.freeze and Object.seal are methods used to control the mutability of objects. They provide different levels of protection against modifications, making it essential to understand their differences when designing your code.

What is Object.freeze?

Definition

Object.freeze is a method that prevents any modifications to an object. Once an object is frozen, you cannot add, remove, or change any of its properties.

Characteristics

• No Changes Allowed: All properties of the object become non-writable, non-configurable, and non-deletable.
• Shallow Freeze: The freeze is shallow, meaning that nested objects are not affected unless they are also explicitly frozen.

Example

What is Object.seal?

Definition

Object.seal is a method that prevents the addition of new properties and marks all existing properties as non-configurable. However, it allows modification of existing property values.

Characteristics

• No New Properties: New properties cannot be added to a sealed object.
• Modifications Allowed: Existing properties can still be modified.
• Shallow Seal: Like Object.freeze, it is also shallow.

Example

Key Differences

1. Modification:
   • Object.freeze: Prevents any modifications to the object, including property changes.
   • Object.seal: Allows changes to existing properties but prevents adding new properties.
2. Use Cases:
   • Object.freeze: Use when you want to create a completely immutable object.
   • Object.seal: Use when you want to restrict object structure but still allow updates to existing properties.
3. Configurability:
   • Object.freeze: Makes all properties non-writable and non-configurable.
   • Object.seal: Makes all properties non-configurable but retains writability.

Conclusion

In summary, Object.freeze provides complete immutability, while Object.seal offers a middle ground by allowing modifications to existing properties but preventing new ones. Understanding these differences will help you effectively manage object mutability in your JavaScript applications.