JavaScript handler.setPrototypeOf() Method

Last Updated : 17 Mar 2025

The handler.setPrototypeOf method returns a Boolean value true if [[Prototype]] was successfully changed. Otherwise, it will return false. It is a trap for Object.setPrototypeOf().

Syntax

Parameters

target: The target object.

prototype: The object's new prototype or null.

Return value

Return a Boolean type value.

Browser Support

Chrome	Compatibility unknown
Edge	Compatibility unknown
Firefox	49
Opera	Compatibility unknown

Example 1

<script>
var pro = { f:13}
var proxy = new Proxy(pro, {
  setPrototypeOf(target, newProto) {
 return newPrototype in target;
  }
});
document.writeln('f' in proxy);
//expected output: true
</script>

Output:

true

Example 2

<script>
var soo={
  foo:1
}
var proxy = new Proxy(soo, {
  setPrototypeOf(target, newProto) {
   
  }
});
document.writeln('a' in proxy); 
//expected output: false
</script>

Output:

false

Example 3

<script>
var xyz = new Proxy({},  {
  setPrototypeOf(target, newProto) {
    if(key == "a") return true;
      return ;false
    }
  }
)	
var first= ("f" in xyz)
var last = ("g" in xyz)
document.write(""+first)
//expected output:false
document.write('<br/>');
document.write("" +last)
//expected output: false
</script>

Output:

false
false

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JavaScript handler.setPrototypeOf() Method

Syntax

Parameters

Return value

Browser Support

Example 1

Example 2

Example 3

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