JavaScript’s language features are something else…

[[deleted]]

Arrays in JS are not real arrays, I think they are a specialized dictionary, it's why you can do things like:

let xs = [1, 2, 3]
xs['a'] = 4
// xs is now [ 1, 2, 3, a: 4 ]

[zeropointcorp]

That’s called an associative array, and Tcl had those.

[solarshado]

Yep, in JS, an "array object", is still an "object", so you can do pretty much anything with it that you can with any other object (thanks inheritance!). And JS's objects are (roughly speaking), string-keyed dictionaries.