call, apply, and bind: Interview Preparation Guide

call, apply, and bind: Interview Preparation Guide

What to Know

1. What each does: call (immediate, comma args), apply (immediate, array args), bind (returns function).
2. How to implement: be able to write polyfills for each.
3. Use cases: method borrowing, fixing this, partial application.
4. Precedence: new > bind > call/apply > implicit > default.
5. Arrows: ignore all three (lexical this).
6. Re-binding: not possible (first bind wins).

Practice Questions

1. Predict the output of code using call/apply/bind.
2. Implement a polyfill for bind.
3. Explain when to use call vs apply vs bind.
4. Fix a lost-this bug using bind.
5. Borrow an array method using call.

Common Interview Format

// Given:
const obj = { x: 10 };
function foo(a, b) { return this.x + a + b; }

// Predict:
foo.call(obj, 1, 2);    // 13
foo.apply(obj, [1, 2]); // 13
const bound = foo.bind(obj, 1);
bound(2);                // 13

The Takeaway

For interviews: know what each does, implement polyfills, know use cases, understand precedence, know arrows ignore them, and know re-binding is not possible. Practice output prediction and polyfill implementation.