javascript - Syntax for setting a variable in javascript

Question

(Edit: I found this syntax while reading someone else's code)

Is there any good reason for using the following syntax for setting a variable in javascript:

this.index >= this.items.length && (this.index = 0);

Is it just to get the expression on one line of code, or is there another, dare I say better, reason for this way of doing it...

Edit: The code is equivalent to:

if (this.index >= this.items.length) { 
    this.index = 0; 
}

score 3 · Accepted Answer

Wow, no. Just no. I consider myself a pretty good JavaScript programmer and I can't tell you what this code does.

Does it just do this.index = this.items.length or does it do something weird like this.index = false?

If you intend:

if (this.index >= this.items.length) {
    this.index = 0;
}

Then you could consider:

this.index = (this.index >= this.items.length) ? 0 : this.index;

But that doesn't really improve it, does it?

score 1 · Accepted Answer

我认为这段代码的意图是

 this.index = this.index >= this.items.length ? this.items.length : 0;

或者

 this.index = this.index >= this.items.length ? 0 : this.items.length;

第三个可能的意图（这可能是它应该做的）。

 this.index = this.index >= this.items.length ? 0 : this.index;

但这只是最好的猜测，这条线根本没有任何意义......而且您通常不会分配这样的变量。实际上它甚至没有分配变量 this.index。

实际上，您的代码确实有效。请参阅此处的工作示例：http: //jsfiddle.net/Elak/EthsP/

在 tbh 之前从未见过这种语法，我写了很多 JavaScript ......但你永远不会停止学习新东西：p

score 1 · Accepted Answer

不，没有充分的理由，我认为人们经常这样做，所以它是一个“单线”，你最好使用if这样的。

if( this.index >= this.items.length ) {
    this.index = 0;
}

因为正如你所看到的，人们对它的实际作用感到困惑。

但你仍然可以像这样保持它的单线

if( this.index >= this.items.length ) { this.index = 0; }

3 回答 3