Polyfill Function.prototype.bind (with new support)

Question

Accepted Answer

**Approach:** Return bound function that handles `new` via `instanceof` check, and concatenates bound args + call args.

```javascript
Function.prototype.myBind = function(thisArg, ...boundArgs) {
  if (typeof this !== 'function') throw new TypeError('myBind called on non-function');
  const target = this;
  function bound(...args) {
    const isNew = this instanceof bound;
    const that = isNew ? this : thisArg;
    return target.apply(that, [...boundArgs, ...args]);
  }
  bound.prototype = Object.create(target.prototype);
  Object.defineProperty(bound, 'length', { value: Math.max(0, target.length - boundArgs.length) });
  return bound;
};

// Demo
function greet(greeting, punct) { return greeting + ' ' + this.name + punct; }
const obj = { name: 'Ada' };
const bound = greet.myBind(obj, 'Hello');
console.log(bound('!')); // Hello Ada!
function Person(name, age) { this.name=name; this.age=age; }
const BoundPerson = Person.myBind(null, 'Bob');
const p = new BoundPerson(30);
console.log(

Polyfill Function.prototype.bind (with new support)

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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.