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JavaScript object freeze vs seal

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JavaScript’s Object.freeze() and Object.seal() methods are used to prevent changes to an object. Object.freeze() creates a read-only object that cannot be modified, while Object.seal() allows modification of existing properties but preventing adding or removing properties.

Object freeze() creates a read-only object by preventing any changes to its properties. Once an object is frozen, you cannot add, remove or modify its properties, and any attempt to do so will result in an error.

Object seal() on the other hand, allows you to modify existing properties of an object but prevents you from adding or removing properties. Once an object is sealed, you cannot add new properties to it or remove existing ones, but you can modify the values of existing properties.

Additionally, the Object.isFrozen() method can be used to determine whether an object is frozen or not. and Object.isSealed() method can be used to determine whether an object is sealed or not.

JavaScript object freeze vs seal examples

Simple example code.

<!DOCTYPE html>

    const objf = {
        prop1: "Hello",
        prop2: "World"


    objf.prop1 = "Hi"; // Throws an error
    delete objf.prop2; // Throws an error

    // seal
    const objs = {
        prop1: "Hello",
        prop2: "World"


    objs.prop1 = "Hi"; // Allowed
    delete objs.prop2; // Throws an error
    objs.prop3 = "New property"; // Throws an error



JavaScript object freeze vs seal

Here is a tabular representation of the differences between Object.freeze() and Object.seal() in JavaScript:

Prevents adding new propertiesYesYes
Prevents deleting propertiesYesYes
Prevents modifying property valuesYesNo
Object.isFrozen() methodAvailableNot applicable
Object.isSealed() methodNot applicableAvailable

Additionally, Object.freeze() provides the Object.isFrozen() method to check if an object is frozen, while Object.seal() provides the Object.isSealed() method to check if an object is sealed.

Comment if you have any doubts or suggestions on this JS difference topic.

Note: The All JS Examples codes are tested on the Firefox browser and the Chrome browser.

OS: Windows 10

Code: HTML 5 Version

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