JavaScript Handler getOwnPropertyDescriptor() Method

JavaScript handler.getOwnPropertyDescriptor() method in Javascript is a trap for the Object.getOwnPropertyDescriptor() method. A property cannot be reported as non-existent if it exists as a non-configurable own property of the target object.

Syntax:

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

Parameters: This method accepts two parameters as mentioned above and described below: 

• Target: This parameter is the target object.
• Prop: This parameter is the name of the property whose description should be retrieved.

Return value: This method returns an object or undefined.

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

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

javascript

const monster1 = {
    num: 4
};

const handler1 = {
    getOwnPropertyDescriptor(target, prop) {
        console.log(`Type : ${prop}`);

        return { configurable: true,
                 enumerable: true,
                 value: 5 };
    }
};

const proxy1 = new Proxy(monster1, handler1);

console.log(Object.getOwnPropertyDescriptor(proxy1, 'num').value);
console.log(Object.getOwnPropertyDescriptor(proxy1, 'bool').enumerable);

Output

Type : num
5
Type : bool
true

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

javascript

const p = new Proxy({ VAL: 20 }, {
    getOwnPropertyDescriptor: function (target, prop) {
        console.log('Property : ' + prop);
        return { configurable: true, enumerable: true, value: 10 };
    }
});

console.log(Object.getOwnPropertyDescriptor(p, 'VAL').value);

const obj = { a: 10 };
Object.preventExtensions(obj);
const pval = new Proxy(obj, {
    getOwnPropertyDescriptor: function (target, prop) {
        return undefined;
    }
});

console.log(Object.getOwnPropertyDescriptor(pval));

Output

Property : VAL
10
undefined

Supported Browsers:

The browsers are supported by handler.getOwnPropertyDescriptor() method is listed below: 

• Google Chrome 49 and above
• Edge 12 and above
• Firefox 18  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.