PlacedElite

Frontend fundamentals set

Eight questions on the JavaScript that frontend interviews actually test — closures, the event loop, this, equality and re-renders.

8 questions ~8 min No account needed

Answer what you can and skip what you cannot — an unanswered question is marked wrong, but guessing teaches you nothing. Marking happens when you submit; nothing is stored against you.

Question 1 of 8 Closures

What does this log? function c() { let n = 0; return () => ++n; } const a = c(), b = c(); console.log(a(), a(), b());

A. 1 2 3 B. 1 2 1 C. 1 1 1 D. 3 3 1

Question 2 of 8 Event loop

What is the output order? console.log("A"); setTimeout(() => console.log("B"), 0); Promise.resolve().then(() => console.log("C")); console.log("D");

A. A B C D B. A D B C C. A C D B D. A D C B

Question 3 of 8 this

Why does an arrow function used as an object method not get the object as `this`?

A. Its `this` comes from the enclosing scope, not from the call B. Arrow functions cannot legally be used as object methods at all C. Arrow functions always set `this` to undefined when invoked D. The object literal has not finished evaluating when it is defined

Question 4 of 8 Equality

Which comparison is TRUE?

A. [1, 2] === [1, 2] B. { a: 1 } === { a: 1 } C. null == undefined D. NaN === NaN

Question 5 of 8 Immutability

State holds an array. You call items.push(x) then setItems(items) and the UI does not update. Why?

A. `push` is asynchronous, so the state had not updated yet B. The array reference did not change, so nothing looks new C. `setItems` only accepts primitive values, never an array D. The list items are missing the `key` prop React requires

Question 6 of 8 Re-renders

Which of these does NOT by itself cause a component to re-render?

A. A module-scope variable it reads is reassigned elsewhere B. Its own component state changes during an event handler C. One of the props passed into it changes to a new value D. Its parent component re-renders for any reason at all

Question 7 of 8 Async

A fetch fails because the user is offline. What is the minimum acceptable behaviour?

A. Nothing — the loading spinner simply keeps on spinning B. Log the error to the console for a developer to find C. Reload the whole page automatically after a short delay D. Show an error saying what failed, and offer a retry

Question 8 of 8 Review

A reviewer has ninety seconds and forty portfolio links. What do they open first?

A. The source files in the GitHub repository, top to bottom B. The installation section of the README, to run it locally C. The live deployed URL, if the project has one D. The commit history

0 of 8 answered