Why do we need “var self = this” in classes in Javascript?

Question

Why can\'t we directly use this instead of self in the following example?

function SeatReservation(name, initialMeal) {
    var self =          


        

Answer 1

There's no reason why you can't use this directly there (and I would say it would be better for readability if you did).

However, the var self = this; is often needed in situations like the following (basically, any asynchronous action like event binding, AJAX handlers etc, where the resolution of this is deferred until it equals something else);

function SeatReservation(name, initialMeal) {
    var self = this;
    self.name = name;
    self.meal = ko.observable(initialMeal);

    setTimeout(function () {
        alert(self.name); // otherwise, this is window; use self to keep a reference to the "SeatReservation" instance.
    }, 100);
}