Pass class function as parameter to another class to use as callback in JavaScript [duplicate]

Question

Alright, so I have two classes. Class 1 contains a specific function, which accesses some of the class' properties. This is what it looks like:

function class1() {
    this.variable = "something";
}

class1.prototype.callback = function() {
    console.log(this.variable); // Returns undefined
}

Class 2 can call any function it is given, and looks like this:

function class2() {}

class2.prototype.caller = function(callback) {
    callback();
}

Then in my regular Javascript I do this:

var c1 = new class1();
var c2 = new class2();
c2.caller(c1.callback);

It is supposed to return "something", however it throws an undefined error. I know it is because it is in the scope of class2 and it is trying to access the variable there, however I have no idea how to get it to execute within the scope of class1.

Any help is greatly appreciated!

Answer 1

Use .bind() or a wrapper function:

c2.caller(c1.callback.bind(c1));

Note that your code was wrong in that it called the function before passing in the return value.

Alternatively:

c2.caller(function() { c1.callback(); });