confused-about-call.js

// I am confused about how you can use `call` without supplying an object for `this`
// The docs don't indicate that you can: 
// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/call

var funny = function (a) { return (a + 3); }
funny(3);           // 6
funny.call({},3);   // 6
funny.call(3);      // NaN  // (as expected)

var xs = [1,2,3]
var pop = Array.prototype.pop;
pop.call(xs);       // 3          // Why does this work ...
pop.call({}, xs);   // undefined  // ... but this does not?

This is fine since xs is your this arg:

pop.call(xs)

But when you call:

pop.call({}, xs)

... it is treating {} as your this arg. But that's not an array, therefore there is nothing to pop off. Also, the xs arg is ignored since pop() doesn't expect any arguments (only expects this).

Ah OK so I was misinterpreting pop as a "pull the last thing off the given array" when it is really "pull that last thing off the array you are attached to". Seems obvious in retrospect - thanks @chilts!