TypeError: can't convert undefined to object — without undefined or object

Question

Consider the code

const arr = [];
[1].map(arr.push)

This gives TypeError: can\'t convert undefined to object (on Firefox at le

Answer 1

That's because arr.push is just a reference to a generic function not bound to arr.

Therefore, when called as a callback, it doesn't know on which array you want to push

var func = [].push;
func(123); // TypeError: can't convert undefined to object

This will work, but multiple arguments will be passed to push, which you probably don't want

const arr = [];
[1, "a"].map(arr.push.bind(arr)); // [ 3, 6 ]
arr; /* [  1,  0, [1, "a"],
         "a",  1, [1, "a"]  ] */

So just use your [1].map(v => arr.push(v))