need explanation of the _.bindAll() function from Underscore.js

Question

I\'ve been learning some backbone.js and I\'ve seen plenty of instances where _.bindAll() is used. I have read through the entire backbone.js and underscore.js docu

Answer 1

var Cow = function(name) {
    this.name = name;
}
Cow.prototype.moo = function() {
    document.getElementById('output').innerHTML += this.name + ' moos' + '
';
}

var cow1 = new Cow('alice');
var cow2 = new Cow('bob');

cow1.moo(); // alice moos
cow2.moo(); // bob moos

var func = cow1.moo;
func(); // not what you expect since the function is called with this===window
_.bindAll(cow1, 'moo');
func = cow1.moo;
func(); // alice moos

Unfortunately the actual "bind all" functionality only works on functions right on the object. To include a function that is defined on the prototype you need to pass those function names explicitely as additional arguments to _.bindAll().

Anyway, you wanted an explanation: Basically it allows you to replace a function on an object with a function that has the same name and behaviour, but is also bound to that object, so this === theObject even without calling it as a method (theObject.method()).