handler.get()

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since September 2016.

The handler.get() method is a trap for the [[Get]] object internal method, which is used by operations such as property accessors.

Try it

const monster = {
  secret: "easily scared",
  eyeCount: 4,
};

const handler = {
  get(target, prop, receiver) {
    if (prop === "secret") {
      return `${target.secret.substring(0, 4)} ... shhhh!`;
    }
    return Reflect.get(...arguments);
  },
};

const proxy = new Proxy(monster, handler);

console.log(proxy.eyeCount);
// Expected output: 4

console.log(proxy.secret);
// Expected output: "easi ... shhhh!"

Syntax

js
new Proxy(target, {
  get(target, property, receiver) {
  }
})

Parameters

The following parameters are passed to the get() method. this is bound to the handler.

target

The target object.

property

A string or Symbol representing the property name.

receiver

The this value for getters; see Reflect.get(). This is usually either the proxy itself or an object that inherits from the proxy.

Return value

The get() method can return any value, representing the property value.

Description

Interceptions

This trap can intercept these operations:

Property access: proxy[foo] and proxy.bar
Reflect.get()

Or any other operation that invokes the [[Get]] internal method.

Invariants

The proxy's [[Get]] internal method throws a TypeError if the handler definition violates one of the following invariants:

The value reported for a property must be the same as the value of the corresponding target object property, if the target object property is a non-writable, non-configurable own data property. That is, if Reflect.getOwnPropertyDescriptor() returns configurable: false, writable: false for the property on target, then the trap must return the same value as the value attribute in the target's property descriptor.
The value reported for a property must be undefined, if the corresponding target object property is a non-configurable own accessor property that has an undefined getter. That is, if Reflect.getOwnPropertyDescriptor() returns configurable: false, get: undefined for the property on target, then the trap must return undefined.

Examples

Trap for getting a property value

The following code traps getting a property value.

js
const p = new Proxy(
  {},
  {
    get(target, property, receiver) {
      console.log(`called: ${property}`);
      return 10;
    },
  },
);

console.log(p.a);
// "called: a"
// 10

The following code violates an invariant.

js
const obj = {};
Object.defineProperty(obj, "a", {
  configurable: false,
  enumerable: false,
  value: 10,
  writable: false,
});

const p = new Proxy(obj, {
  get(target, property) {
    return 20;
  },
});

p.a; // TypeError is thrown