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JavaScript handler set() Method

JavaScript handler set() Method with examples on javascript handler, javascript methods, javascript tutorial, apply(), construct(), defineProperty(), deleteProperty(), get(), setPrototypeOf(), set(), ownKeys(), isExtensible() etc.

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JavaScripthand handler.set() Method

The handler.set method is an assignment of a value to a property value. The set can be iterator in the insertion order. It is a collection of items which are unique. If an assignment succeeded, then return true. Otherwise, returns false.

An Iterator is an object which defines a sequence and potentially a return value upon its termination.

Syntax

set: function(target, property, value, receiver)

Parameters

target: The target object.

property: Name or Symbol of the property.

value: New value of the property.

receiver: This is usually the proxy itself. A set handler assignment indirectly, via the prototype chain or various other ways.

Return value

Return a Boolean value.

Browser Support

Chrome 49
Edge 12
Firefox 18
Opera 36

Example 1

<script>
var proxy = { "a": 1, "b": 2 }
var pset = new Proxy(
  proxy, {
    set: function(y, idx, value) {
    y[idx] = value * 10
   }
  }
)
pset.c = 3
for(var z in pset) {
  document.writeln(z + "=" )
  // print equal sign.
  document.writeln(pset[z])
  
  //expected output: a= 1 b= 2 c= 30
}
</script>
Test it Now

Output:

a= 1 b= 2 c= 30

Example 2

<script>
var x = { foo: 1 };
var proxy = new Proxy(x, {
  set: function(target, name, value, proxy) {
  document.writeln ('in set');
target[name] = value.toUpperCase();
  }
});
proxy.foo = 'proxy method';
document.writeln(x.foo); // value stored on x is uppercase
 //expected output: in set PROXY METHOD
 </script>
Test it Now

Output:

in set PROXY METHOD

Example 3

<script>
const q={
 foo:1
}
const p = new Proxy(q, {
  set: function(target, prop, value, receiver) {
    target[prop] = value;
    document.writeln('property set: ' + prop + ' = ' + value);
    //expected output: property set: a = 10
    }
})
document.writeln('a' in p); 
//expected output: false
p.a = 10;  
// "property set: a = 10"
</script>
Test it Now

Output:

false property set: a = 10

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