Function.prototype.call

easycodingJavaScriptFunctionsPrototypes~10 min

Asked at Google, Meta, Amazon

Overview

Implement fnCall(fn, thisArg, ...args) that simulates fn.call(thisArg, ...args).

Constraints

Do not use Function.prototype.call or Function.prototype.apply.

Examples

function greet(greeting) { return greeting + ' ' + this.name; }
fnCall(greet, { name: 'Bob' }, 'Hi'); // 'Hi Bob'

Solution

Reveal solution

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

function-prototype-call.js

Function.prototype.call

easycodingJavaScriptFunctions

Overview

Implement fnCall(fn, thisArg, ...args) that simulates fn.call(thisArg, ...args).

Constraints

Do not use Function.prototype.call or Function.prototype.apply.

Examples

function greet(greeting) { return greeting + ' ' + this.name; }
fnCall(greet, { name: 'Bob' }, 'Hi'); // 'Hi Bob'

Solution

Reveal solution

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

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