为什么我们需要“var self = this"?在 Javascript 类中? [英] Why do we need "var self = this" in classes in Javascript?

问题描述

为什么我们不能在下面的例子中直接使用this而不是self?

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

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

回复后，我了解到:

是的，如果课堂上没有上下文切换，则不需要.

Yes, there is no need if there is no context switch in class.

但我将使用这种方法作为约定"，尽管没有必要.

But I will use this approach as "convention" although there is no need.

推荐答案

没有理由为什么你不能直接在那里使用 this(我会说它会如果你做了，那么可读性会更好).

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).

然而，var self = this; 通常在以下情况下需要(基本上，任何异步操作，如事件绑定、AJAX 处理程序等，其中 this被推迟直到它等于其他东西);

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);
}

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