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JavaScript Object.preventExtensions() Method

  • Last Updated : 23 Sep, 2021

The Object.preventExtensions() method in JavaScript is standard built-in objects which prevents new properties from ever being added to an object.
Syntax: 
 

Object.preventExtensions( obj )

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

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  • 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: 
 

javascript




let geeks1 = {};
   
Object.preventExtensions(geeks1);
   
try {
  Object.defineProperty(geeks1, 'prop1', {
    value: "GFG",
    property1:"Geeksforgeeks",
    property2:"Best platform to learn"
  });
} catch (error) {
  console.log(error);
}

Output: 
 



TypeError: Cannot define property prop1, object is not extensible

Example 2: 
 

javascript




var geeks = {};
var geeks0 = Object.preventExtensions(geeks);
console.log( geeks0 === geeks);
  
const geeks1 = {"prop1": 555}; 
Object.preventExtensions(geeks1); 
delete geeks1.prop1; 
console.log ( geeks1.hasOwnProperty ( "prop1" ) );
  
const geeks2 = {}; 
Object.preventExtensions(geeks2); 
geeks2.prop2 = 3; 
    
console.log( 
    geeks2.hasOwnProperty("prop2"
);  
  
const geeks3 = {}; 
Object.preventExtensions(geeks3); 
console.log( 
    Object.isExtensible(geeks3) 
);

Output: 
 

true
false
false
false

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

  • Chrome 6 and above
  • Edge 12 and above
  • Firefox 4 and above
  • Internet Explorer 9 and above
  • Opera 12 and above
  • safari 5.1 and above



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