Array forEach pass “push” as argument

Question

Faced strange issue in JS. I receive error on this:

let a = []
let b = [1,2,3]
b.forEach(a.push)
TypeError: Array.prototype.push called on null or undefined
             


        

Answer 1

Because .forEach() supplies to your callback 3 arguments.

callback is invoked with three arguments:

1. the element value
2. the element index
3. the array being traversed

The .push() can accept any number of arguments. So, on each iteration, .push() adds those three arguments to your array.