JS: Reflect.set

(new in ECMAScript 2015)

Reflect.set(obj, key, val)

• Set a value to a proprety of object.
• Return true if success, else false.

🟢 tip: This function is similar to the syntax obj[key] = val, but in a function form. [see JS: Function Form vs Operator]

const xx = {};
Reflect.set(xx, "dog", 3);
console.assert(Object.hasOwn(xx, "dog"));
console.assert(xx["dog"] === 3);

// example of failed attempt to set property

const xx = {};
Object.preventExtensions(xx);
console.assert(Reflect.set(xx, "dog", 3) === false);
console.assert(Object.hasOwn(xx, "dog") === false);

Reflect.set(obj, key, val, thisValue)

if the property is a setter property, thisValue is passed to the setter function as this-binding. If not a setter property, thisValue is ignored.

• JS: Getter Setter Property (accessor)

// apple. has a setter property named color.
// it stores value to color_val.
const apple = {
 color_val: "",
 set color(x) {
  this.color_val = x;
 },
};

// grape. has a property named color_val.
const grape = { color_val: "" };

// set apple.color to green
Reflect.set(apple, "color", "green");

// check
console.assert(
 apple.color_val === "green",
);

// set setter method apple.color to red, but on object grape
Reflect.set(apple, "color", "red", grape);

// check
console.assert(
 grape.color_val === "red",
);