JS: Function.prototype.bind

f.bind(obj) → return a function such that it has the same behavior as f except f's this value is always obj.

[see JS: “this” Binding]

f.bind(obj, args …) → the new function will always be given the arguments args.

// example of using Function.prototype.bind

// object with 1 property ff.
const aa = { "ff":function () { return this;} };

// new object bb
const bb = {"b":2};

// create a new function, that is ff with thisBinding of bb
const gg = aa.ff.bind(bb);

console.log( gg() ); // { b: 2}

Example of using Function.prototype.bind with default argument:

// Example of using Function.prototype.bind with default argument

function ff(x) { this["p"] = x; };

const bb = {"b":2};

// create a new function
// with default ThisBinding and a default arg
const gg = ff.bind(bb,7);

// call gg
gg();
// note, no args are given.

console.log( bb ); // { b: 2, p: 7 }

Reference

ECMAScript 2015 §Fundamental Objects#sec-function.prototype.bind