Polyfill Function.prototype.call and apply

Question

Accepted Answer

**Approach:** Temporarily assign function as property on context object using Symbol key, invoke, delete.

```javascript
Function.prototype.myCall = function(thisArg, ...args) {
  if (typeof this !== 'function') throw new TypeError('myCall on non-function');
  const ctx = thisArg == null ? globalThis : Object(thisArg);
  const key = Symbol('fn');
  ctx[key] = this;
  const result = ctx[key](...args);
  delete ctx[key];
  return result;
};
Function.prototype.myApply = function(thisArg, argsArray) {
  if (typeof this !== 'function') throw new TypeError('myApply on non-function');
  const ctx = thisArg == null ? globalThis : Object(thisArg);
  const key = Symbol('fn');
  ctx[key] = this;
  const result = argsArray ? ctx[key](...argsArray) : ctx[key]();
  delete ctx[key];
  return result;
};

// Demo
function greet(greeting, punct){ return `${greeting} ${this.name}${punct}`; }
const ctx = { name: 'Grace' };
console.log(greet.myCall(ctx, 'Hi', '!')); // Hi Grace!
console.log(greet.myApply(c

Polyfill Function.prototype.call and apply

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Understand the problem

Attempt it yourself

Study the solution

Solution ready — 2 min read

Join the discussion

Discussion (0)

KEEP THESTREAK ALIVE.

KEEP THE
STREAK ALIVE.