＆是什么QUOT; this._events || （this._events = {}）;＆QUOT;意思？ [英] What does "this._events || (this._events = {});" mean?

问题描述

我已经开始学习Backbone.js的。目前我的JavaScript技能并不太好。我已经开始检查 Backbone.js的文件和所遇到的code，其目的我不能想出了一个奇怪的线。 code样本（如果你需要更多的情况下，手动下载 Backbone.js的为开发者和看行80 ）：

I have started learning Backbone.js. Currently my JavaScript skills are not too good. I have started to examine the backbone.js file and have come across a strange line of code whose purpose I can not figure out. Code sample (if you need more context, manually download backbone.js for developers and see line 80):

var Events = Backbone.Events = {

  // Bind an event to a `callback` function. Passing `"all"` will bind
  // the callback to all events fired.
  on: function(name, callback, context) {
    if (!eventsApi(this, 'on', name, [callback, context]) || !callback) return this;
    this._events || (this._events = {});
    var events = this._events[name] || (this._events[name] = []);
    events.push({callback: callback, context: context, ctx: context || this});
    return this;
  },

这是什么行 this._events || （this._events = {}）; 是什么意思？对我来说， _events 看起来像一个内部变量，但（this._events = {}）用于转让或它是一个或比较呢？或者是 || 在这种情况下完全不同的操作？

What does the line this._events || (this._events = {}); mean? For me, _events looks like an inner variable, but is (this._events = {}) used for assignment or is it an or comparison? Or is || a completely different operation in this context?

推荐答案

这是一个使用JavaScript的falsy的评价一招。它是一样的：

It is a trick that uses javascripts "falsy" evaluation. It is the same as:

if (this._events) {
    // do nothing, this._events is already defined
} else {
    this._events = {};
}

这同样适用于行 VAR的事件= this._events [名] || （this._events [名] = []）; 这可以转换为

var events;
if (this._events[name]) {
    events = this._events[name];
} else {
    this._events[name] = [];
    events = this._events[name];
}

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