`this` manipulation in JavaScript

this.js

var slice = [].slice

var array = []
console.log(array.push)

var object = {
    f: function (x, y) {
        var vargs = slice.call(arguments)
        console.log(this.i, x, y)
    },
    i: 2
}

object.f(1, 3)

var f = object.f

/* nothing_here. */ f(1, 3) // <- ? `undefiend`


f.call(object, 1, 3)
f.apply(object, [ 1, 3 ])

var a = []

a[0] = 1
a = a.concat(3)

f.apply(object, a)

var thingamabob = {
    f: f.bind(object, 7),
    i: 4
}

function sum (a, b) { return a + b }

var add7 = sum.bind(null, 7)
                       // ^j

console.log(add7(3))

thingamabob.f(1, 3)
// ?, 1, 3

array.reduce(function (prev, next) {
    this.
}.bind(this)