Function.prototype.apply

easycodingJavaScriptFunctionsPrototypes~10 min

Asked at Google, Meta, Amazon

Overview

Implement fnApply(fn, thisArg, args) that simulates fn.apply(thisArg, args).

Constraints

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

Examples

function greet(greeting) { return greeting + ' ' + this.name; }
fnApply(greet, { name: 'Alice' }, ['Hello']); // 'Hello Alice'

Solution

Reveal solution

function fnApply(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-apply.js

Function.prototype.apply

easycodingJavaScriptFunctions

Overview

Implement fnApply(fn, thisArg, args) that simulates fn.apply(thisArg, args).

Constraints

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

Examples

function greet(greeting) { return greeting + ' ' + this.name; }
fnApply(greet, { name: 'Alice' }, ['Hello']); // 'Hello Alice'

Solution

Reveal solution

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

NameTopicDifficulty

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