JavaScript Object preventExtensions() Method

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The Object.preventExtensions() method in JavaScript is a standard built-in object which prevents new properties from ever being added to an object. This method also prevents reassigning of the object’s prototype.

Syntax:

Object.preventExtensions( obj )

Parameters: This method accepts a single parameter as mentioned above and described below:

obj: This parameter holds the object which must be made non-extensible.

Return value: This method returns the object after making it non-extensible.

Below examples illustrate the Object.preventExtensions() method in JavaScript:

Example 1: This example throws a type error as we cannot assign new properties to the object because Object.preventExtensions() method is used.

javascript

let zambiatek1 = {}; 
  
Object.preventExtensions(zambiatek1); 
  
try { 
    Object.defineProperty(zambiatek1, 'prop1', { 
        value: "GFG", 
        property1: "Geeksforzambiatek", 
        property2: "Best platform to learn"
    }); 
} catch (error) { 
    console.log(error); 
}

Output:

TypeError: Cannot define property prop1, object is not extensible

Example 2: In this example, we will check if we have some properties of the object or not using the Object.hasOwnProperty() method with the Object.preventExtensions() method.

javascript

let zambiatek = {}; 
let zambiatek0 = Object.preventExtensions(zambiatek); 
console.log(zambiatek0 === zambiatek); 
  
const zambiatek1 = { "prop1": 555 }; 
Object.preventExtensions(zambiatek1); 
delete zambiatek1.prop1; 
console.log(zambiatek1.hasOwnProperty("prop1")); 
  
const zambiatek2 = {}; 
Object.preventExtensions(zambiatek2); 
zambiatek2.prop2 = 3; 
  
console.log( 
    zambiatek2.hasOwnProperty("prop2") 
); 
  
const zambiatek3 = {}; 
Object.preventExtensions(zambiatek3); 
console.log( 
    Object.isExtensible(zambiatek3) 
);

Output:

true
false
false
false

We have a complete list of Javascript Object methods, to check those please go through this JavaScript Object Complete Reference article.

Supported Browsers: The browsers supported by Object.preventExtensions() method are listed below:

Chrome 6 and above
Edge 12 and above
Firefox 4 and above
Opera 12 and above
safari 5.1 and above

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