Function.prototype.bind

easycodingJavaScriptFunctionsPrototypes~10 min

Asked at Meta, Google, Stripe

Overview

Implement fnBind(fn, thisArg, ...boundArgs) that returns a new function with this bound to thisArg and initial arguments pre-filled.

Constraints

Do not use Function.prototype.bind.

Examples

function add(a, b) { return this.x + a + b; }
const bound = fnBind(add, { x: 10 }, 1);
bound(2); // 13

Solution

Reveal solution

function fnBind(fn, thisArg, ...boundArgs) {
  return function(...args) {
    const ctx = Object(thisArg);
    const key = Symbol();
    ctx[key] = fn;
    const result = ctx[key](...boundArgs, ...args);
    delete ctx[key];
    return result;
  };
}

function-prototype-bind.js

Function.prototype.bind

easycodingJavaScriptFunctions

Overview

Implement fnBind(fn, thisArg, ...boundArgs) that returns a new function with this bound to thisArg and initial arguments pre-filled.

Constraints

Do not use Function.prototype.bind.

Examples

function add(a, b) { return this.x + a + b; }
const bound = fnBind(add, { x: 10 }, 1);
bound(2); // 13

Solution

Reveal solution

function fnBind(fn, thisArg, ...boundArgs) {
  return function(...args) {
    const ctx = Object(thisArg);
    const key = Symbol();
    ctx[key] = fn;
    const result = ctx[key](...boundArgs, ...args);
    delete ctx[key];
    return result;
  };
}

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