JS: Reflect.get

New in JS2015.

Reflect.get(obj, key)

Return the value of a property, own property or in Prototype Chain.

• If key is not found, return undefined.
• If obj is not Object Type object, throw a TypeError exception.

This function is similar to the syntax obj[key], but in a function form. Function form lets you easily manipulate it at run-time.

const jj = { k: 3 };

console.log(Reflect.get(jj, "k") === 3);

// if property key is not found, return undefined
console.log(Reflect.get(jj, "h") === undefined);

// Reflect.get looks up prototype chain

const xx = { p: 3 };
const yy = {};

Object.setPrototypeOf(yy, xx);
// x is parent of y

console.log(Reflect.get(yy, "p") === 3);

Reflect.get(obj, key , thisValue)

thisValue is passed as this Binding to a getter property call.

〔see Getter Setter Properties〕

Getter Property and ThisValue Example

// create a object with 2 properties: p1 and p2. The p2 is a getter property.
const xx = {
  p1: 1,
  get p2() {
    console.log("getter called");
    return this.p1;
  },
};

// create some unrelated object with key p1
const yy = { p1: "wow" };

console.log(
  Reflect.get(xx, "p2", yy) === "wow",
);
// prints "getter called"

〔see Getter Setter Properties〕