JavaScript Flashcards

What does the `typeof` operator return for `null`?

Answer: 'object'

`typeof null` returns `'object'` due to a long-standing bug in JavaScript that was never fixed for backwards compatibility.

Which method removes the last element from an array and returns it?

Answer: pop()

`Array.prototype.pop()` removes and returns the last element, mutating the original array.

What is the output of `console.log(0.1 + 0.2 === 0.3)` in JavaScript?

Answer: false

Floating-point arithmetic in JavaScript produces `0.30000000000000004`, so the strict equality check returns `false`.

What does the `Array.from()` method do?

Answer: Creates a new Array instance from an array-like or iterable object

`Array.from()` creates a new array from array-like objects (e.g., NodeLists, strings) or iterables.

What is a closure in JavaScript?

Answer: A function that retains access to its lexical scope even after the outer function has returned

A closure is created when an inner function captures and remembers variables from its surrounding scope.

Which statement correctly declares a block-scoped variable in modern JavaScript?

Answer: let x = 5;

`let` declares a block-scoped variable, unlike `var` which is function-scoped.

What does `JSON.stringify()` do when it encounters a function value in an object?

Answer: Omits the key entirely

`JSON.stringify()` silently omits object properties whose values are functions because JSON has no function type.