jQuery源代码中的returnTrue和returnFalse函数 [英] returnTrue and returnFalse functions in jQuery source

问题描述

我不禁注意到jQuery的源代码中有两个看似无用的函数（对于v1.9.1，它的第2702行和第2706行）：

I can't help but notice there are two seemingly useless functions in the source code of jQuery (For v1.9.1, it's line 2702 and line 2706):

function returnTrue() {
    return true;
}

function returnFalse() {
    return false;
}

在jQuery中经常调用它们。有没有理由说他们不能简单地用布尔 true 或 false 替换函数调用？

Which both are called quite often within jQuery. Is there a reason why they don't simply substitute the function call with a boolean true or false?

推荐答案

它的使用方式如下：

stopImmediatePropagation: function() {
    this.isImmediatePropagationStopped = returnTrue;
    this.stopPropagation();
}

此处 isImmediatePropagationStopped 是查询方法。像这样使用 event.isImmediatePropagationStopped（）

here isImmediatePropagationStopped is a query method. used like this event.isImmediatePropagationStopped()

当然，你可以定义一个实例方法，如：

of course, you can define a instance method, like:

event.prototyoe.isImmediatePropagationStopped = function() { return this._isImmediatePropagationStopped };

stopImmediatePropagation: function() {
    this._isImmediatePropagationStopped = true; //or false at other place.
    this.stopPropagation();
}

但你必须引入一个新的实例属性 _isImmediatePropagationStopped 存储状态。

but you have to introduce a new instance property _isImmediatePropagationStopped to store the status.

有了这个技巧，你可以在这里切断一堆实例属性for hold true / false status，比如 _isImmediatePropagationStopped ， _isDefaultPrevented 等。

with this trick, you can cut off bunch of instance properties for hold true/false status here, like _isImmediatePropagationStopped, _isDefaultPrevented etc.

因此，在我看来，这只是代码风格的问题，不是对或错。

so that, in my opinion, this is just a matter of code style, not right or wrong.

PS：事件的查询方法，如 isDefaultPrevented ， isPropagationStopped ， isImmediatePropagationStopped 在DOM事件级别3 sepc中定义。

PS: the query methods on event, like isDefaultPrevented , isPropagationStopped, isImmediatePropagationStopped are defined in DOM event level 3 sepc.

spec： http://www.w3.org/TR/2003/NOTE-DOM-Level-3-Events-20031107/events.html#Events-Event-isImmediatePropagationStopped

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