var self = this?

Question

Using instance methods as callbacks for event handlers changes the scope of this from \"My instance\" to \"Whatever just called the callback\"

Answer 1

This question is not specific to jQuery, but specific to JavaScript in general. The core problem is how to "channel" a variable in embedded functions. This is the example:

var abc = 1; // we want to use this variable in embedded functions

function xyz(){
  console.log(abc); // it is available here!
  function qwe(){
    console.log(abc); // it is available here too!
  }
  ...
};

This technique relies on using a closure. But it doesn't work with this because this is a pseudo variable that may change from scope to scope dynamically:

// we want to use "this" variable in embedded functions

function xyz(){
  // "this" is different here!
  console.log(this); // not what we wanted!
  function qwe(){
    // "this" is different here too!
    console.log(this); // not what we wanted!
  }
  ...
};

What can we do? Assign it to some variable and use it through the alias:

var abc = this; // we want to use this variable in embedded functions

function xyz(){
  // "this" is different here! --- but we don't care!
  console.log(abc); // now it is the right object!
  function qwe(){
    // "this" is different here too! --- but we don't care!
    console.log(abc); // it is the right object here too!
  }
  ...
};

this is not unique in this respect: arguments is the other pseudo variable that should be treated the same way — by aliasing.