JavaScript handler.has() Method

The handler.has() method used to "hide" any property you want. It's a trap for an operator. It returns the Boolean value true if you want the property to be accessed, otherwise false If the key is present or not in the original object.

Syntax

Parameters

target: The target object.

prop: The property to check for existence.

Return value

Return a Boolean value.

Browser Support

Chrome	49
Edge	12
Firefox	18
Opera	36

Example 1

const x = { f:10 };
const proxy = new Proxy(x, {
  has: function(target, name) {
   document.writeln('in has');
     //expected output: in has
 return name in target;
  }
});
document.writeln('f' in proxy);
//expected output: true

Test it Now

Output:

in has true

Example 2

var x={hoo:1}
var xyz = new Proxy(x,  {
  has: function(target, key) {
    if(key == "a") return false;
      return true;
    }
  }
)
var x= ("a" in xyz)	
var y = ("b" in xyz)	
document.write("a in d: " +x)
//expected output: a in d: false
document.write('<br/>');
document.write("b in d: " +y) 
//expected output: b in d: true

Test it Now

Output:

a in d: false
b in d: true

Example 3

var s={
  voo:1
}
var p = new Proxy(s, {
  has: function(target, prop) {
    document.writeln('called: ' + prop);
    return false;
  }
});
document.writeln('a' in p); 
//expected output:called: a false

Test it Now

Output: