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JavaScript | handler.construct() Method

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  • Last Updated : 27 Sep, 2021
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The handler.construct() method in JavaScript is a trap for the new operation and this method returns an object.
Syntax: 
 

const p = new Proxy(target, {
  construct: function(target, argumentsList, newTarget) {
  }
});  

Parameters: This method accept three parameters as mentioned above and described below: 
 

  • Target: This parameter holds the target object.
  • argumentsList: This parameter holds the list of the constructor.
  • newTarget: This parameter holds the constructor that was originally called, p above.

Return value: This method returns an object.
Below examples illustrate the handler.construct() method in JavaScript:
Example 1: 
 

javascript




<script>
function monster1(disposition) {
  this.disposition = disposition;
}
 
const handler1 = {
  construct(target, args) {
    console.log('Users at Geeksforgeeks are called');
 
    return new target(...args);
  }
};
 
const proxy1 = new Proxy(monster1, handler1);
console.log(new proxy1('Geeks').disposition);
 
var pro = new Proxy(function() 
                    {}, { 
  construct: function(objTarget, args, oldConstructor) { 
     return { Value : args[0] + " to anybody" }  
  
}) 
   
console.log(JSON.stringify(new pro("Hello "), null, ' ')) 
</script>

Output: 
 

"Users at Geeksforgeeks are called"
"Geeks"
"{
 "Value": "Hello  to anybody"
}"

Example 2: 
 

javascript




<script>
const p = new Proxy(function() {}, {
  construct: function(target, argumentsList, newTarget) {
    console.log('Value: ' + argumentsList.join(', '));
    return { value: argumentsList[0] * 10 /3};
  }
});
 
console.log('New Value: ' +new p(4).value);
</script>

Output: 
 

"Value: 4"
"New Value: 13.333333333333334"

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

  • Google Chrome 49 and above
  • Firefox 18 and above
  • Opera 36 and above
  • Safari 10 and above
  • Edge 12 and above

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