JS: Reflect.apply (λ)

By Xah Lee. Date: 2017-02-12. Last updated: 2026-01-21.

(new in ECMAScript 2015)

Reflect.apply(f, thisBinding, argArray)

Call f with this (binding) of thisBinding, and with arguments of elements in argArray.
Return the result.
argArray is array or Array-Like Object.

function ff(a, b) {
 return a + b;
}
console.log(Reflect.apply(ff, null, [1, 2]));
// 3

// apply an arrow function
console.log(Reflect.apply(((a, b) => (a + b)), null, [1, 2]));
// 3

// example of Reflect.apply with thisBinding argument

function ff(a, b) {
 this.k1 = a;
 this.k2 = b;
}

const jj = {};

Reflect.apply(ff, jj, [3, 4]);

console.log(jj);
// { k1: 3, k2: 4 }

Purpose of Reflect.apply

Reflect.apply is created in ECMAScript 2015. It fixes some problem of

because

Function.prototype.apply is confusing, because the actual call form is fName.apply. You need to understand this-binding and inheritance mechanism of JavaScript. Also, the dotted object/property relation is not the object parent/child relation. 〔see JS: Prototype and Inheritance〕
Function.prototype.apply does not work if a function has a property "apply" or in its parent chain.
Reflect.apply does not have these problems.

/*
comparison of
Reflect.apply
vs
Function.prototype.apply
*/

console.log(Reflect.apply(Math.max, null, [24, 185, 53]));
// 185

console.log(Math.max.apply(null, [24, 185, 53]));
// 185

JS: Reflect.apply (λ)

Purpose of Reflect.apply

JavaScript. Apply Function