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
    at Array.forEach (native)
    at repl:1:3
    at REPLServer.defaultEval (repl.js:262:27)
    at bound (domain.js:287:14)
    at REPLServer.runBound [as eval] (domain.js:300:12)
    at REPLServer.<anonymous> (repl.js:431:12)
    at emitOne (events.js:82:20)
    at REPLServer.emit (events.js:169:7)
    at REPLServer.Interface._onLine (readline.js:211:10)
    at REPLServer.Interface._line (readline.js:550:8)

```

Sure, I've made a suggestion, that the context is lost. So, I try to accomplish that in this way:

```
b.forEach([].push.bind(a))

```

The result becomes unpredictable:

```
[ 1, 0, [ 1, 2, 3 ], 2, 1, [ 1, 2, 3 ], 3, 2, [ 1, 2, 3 ] ]

```

WHAT? =) Where is 0 from? Okay, maybe its "glitch"-index, but why not first than? :)

Just to make it clear, this works in a classical way, and that's not a question:

```
b.forEach(el => a.push(el) )

```

Can someone explain this strange behaviour?