Symbol.iterator — JS Technical Interview Questions & Answers

The well-known symbol that makes a value iterable.

Symbol.iterator

  • Symbol.iterator is a JS topic. In plain words you use it for a short Symbol.iterator example in a script in the browser. Don’t start with a slogan — start with that picture.
  • Smallest example: the smallest Symbol.iterator example you can type. Type it, run it, and say what you see. If you can do that from memory, you know Symbol.iterator.
  • From the example next to this theory: The well-known symbol that makes a value iterable.
  • Trap: only saying “Symbol.iterator” with no example. Fix that before you talk about advanced JS.
  • Viva: what is Symbol.iterator? Then show the smallest Symbol.iterator example you can type. Then name the trap.

Technical Interview Tip: What is Symbol.iterator? Show this: the smallest Symbol.iterator example you can type. Trap: only saying “Symbol.iterator” with no example.

Code Examples for Symbol.iterator

Symbol.iterator — working example

const nums = [10, 20];
console.log(...nums);

const range = {
  from: 1,
  to: 3,
  [Symbol.iterator]() {
    let n = this.from;
    const last = this.to;
    return {
      next() {
        if (n <= last) return { value: n++, done: false };
        return { done: true };
      },
    };
  },
};
console.log([...range]);

Symbol.iterator — for...of and spread use the iterable protocol (Symbol.iterator → next()).

How to Explain Symbol.iterator to an Interviewer

What is Symbol.iterator?

Used for a short Symbol.iterator example a script in the browser Not just the heading

Give one small example of Symbol.iterator.

the smallest Symbol.iterator example you can type The well-known symbol that makes a value iterable

What mistake do beginners make with Symbol.iterator?

only saying “Symbol.iterator” with no example Show the fix

Where do you use Symbol.iterator?

a script in the browser a short Symbol.iterator example