classList API — JS Technical Interview Questions & Answers

add, remove, toggle and contains for CSS classes.

classList API

  • classList API (js dom) is a JS topic. In plain words you use it for click Save in a form page. Don’t start with a slogan — start with that picture.
  • Smallest example: addEventListener('click', …). Type it, run it, and say what you see. If you can do that from memory, you know classList API (js dom).
  • From the example next to this theory: add, remove, toggle and contains for CSS classes.
  • Trap: listener on a node that gets replaced. Fix that before you talk about advanced JS.
  • Viva: what is classList API (js dom)? Then show addEventListener('click', …). Then name the trap.

Technical Interview Tip: What is classList API (js dom)? Show this: addEventListener('click', …). Trap: listener on a node that gets replaced.

Code Examples for classList API

classList API — working example

// Browser DOM sketch:
// const el = document.querySelector("#title");
// el.textContent = "Updated";
// el.setAttribute("data-ok", "1");
// el.classList.add("active");

// Runnable stand-in for Node/Piston:
const el = { textContent: "Hello", className: "title", attrs: {} };
el.textContent = "Updated";
el.attrs["data-ok"] = "1";
el.className += " active";
console.log(el);

classList API — the DOM is the live document tree. Select nodes, then change text, attributes, classes, or structure.

How to Explain classList API to an Interviewer

What is classList API (js dom)?

Used for click Save a form page Not just the heading

Give one small example of classList API (js dom).

addEventListener('click', …) add, remove, toggle and contains for CSS classes

What mistake do beginners make with classList API (js dom)?

listener on a node that gets replaced Show the fix

Where do you use classList API (js dom)?

a form page click Save