JavaScript Basics Flashcards

Question 1

JS: what is the difference between == and ===?

Accepted Answer

=== compares without type coercion (strict equality); == coerces types first

Question 2

JS: transform every element of an array?

Accepted Answer

array.map(x => ...)

Question 3

JS: keep only elements matching a condition?

Accepted Answer

array.filter(x => condition)

Question 4

JS: reduce an array to a single value?

Accepted Answer

array.reduce((acc, x) => ..., initial)

Question 5

JS: what does const prevent?

Accepted Answer

Reassignment of the binding — object contents can still mutate

Question 6

JS: syntax for an async function that awaits a fetch?

Accepted Answer

async function f() { const res = await fetch(url); }

Question 7

JS: check if a value is an array?

Accepted Answer

Array.isArray(value)

Question 8

JS: what is a closure?

Accepted Answer

A function that retains access to variables from the scope where it was created

Question 9

JS: spread an array into a new one?

Accepted Answer

const copy = [...original]

Question 10

JS: what does JSON.stringify do?

Accepted Answer

Serializes a value to a JSON string

Free JavaScript Basics Flashcards