JavaScript Handler preventExtensions() Method

JavaScript handler.preventExtensions() method in JavaScript is a trap for Object.preventExtensions() method. New properties cannot be added to an object when extensions are disabled. It returns a boolean value.

Syntax: 

const p = new Proxy(target, {
 preventExtensions: function(target) {
 }
});

Parameters: This method accepts a single parameter target that holds the target object.

Return value: This method returns a boolean value.

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

Example 1: In this example, we will see the use of the handler.preventExtensions() method in JavaScript.

Output: 

true
[object Object]
false
true

Example 2: In this example, we will see the use of the handler.preventExtensions() method in JavaScript.

Output: 

preventExtensions()
[object Object]
[object Object]
false
false

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

• Google Chrome 49 and above
• Edge 12 and above
• Firefox 22 and above
• Opera 36 and above
• Safari 10 and above

We have a complete list of Javascript Proxy/handler methods, to check those go through the Javascript Proxy/handler Reference article.