JavaScript handler.defineProperty() method in Javascript is used to define the new properties and to modify the existing properties directly on an object. It is a trap for Object.defineProper().
Syntax:
const p = new Proxy(target, {
defineProperty: function(target, property, descriptor) {
}
});
Parameters: This method accepts three parameters as mentioned above and described below:
- Target: This parameter holds the target object.
- property: This parameter is the name or Symbol of the property whose description is going to be retrieved..
- descriptor: This parameter is the descriptor for the property being defined or modified.
Return value: This method returns a Boolean value which is used to indicate if the property is successfully defined.
Below example illustrates the handler.defineProperty() method in JavaScript:
Example 1: In this example, we will see the use of the handler.defineProperty() method in JavaScript.
javascript
const p = new Proxy({}, { defineProperty: function (target, prop, descriptor) { console.log('Type : ' + prop); return true; }});const desc = { configurable: true, enumerable: true, value: 10 };Object.defineProperty(p, 'String', desc);let xyz = {};let proxy = new Proxy(xyz, { defineProperty: function (target, name, propertyDescriptor) { console.log('in defineProperty'); return Object.defineProperty(target, name, propertyDescriptor); }});Object.defineProperty(proxy, 'bar', {}); |
Output:
"Type : String" "in defineProperty"
Example 2: In this example, we will see the use of the handler.defineProperty() method in JavaScript.
javascript
const handler1 = { defineProperty(target, key, descriptor) { invariant(key, 'define'); return true; }};function invariant(key, action) { if (key[0] === '_') { throw new Error( `Invalid attempt to ${action} private "${key}" property`); }}const monster1 = {};const proxy1 = new Proxy(monster1, handler1);console.log(proxy1._propt = 'Handler defineProperty'); |
Output:
Error: Invalid attempt to define private "_propt" property
Supported Browsers: The browsers supported by handler.defineProperty() 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
We have a complete list of Javascript Proxy/handler methods, to check those go through the Javascript Proxy/handler Reference article.
