javascript operator “in”

Question

I\'m used to python, so

a = [1,2,3]
1 in a # -> True
b = [\"1\", \"2\", \"3\", \"x\"]
\"x\" in b # -> True

Why is it that in JavaScript

Answer 1

in works on KEYS of arrays, not values. 1 in a succeeds because there is an element #1 in your array, which is actually the 2 value.

"1" fails, because there is no 1 PROPERTY or KEY in your array.

Details here: https://developer.mozilla.org/en/JavaScript/Reference/Operators/in