Javascript 双感叹号是什么！！运营商是什么意思？
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What does the double exclamation !! operator mean?
提问by stirfries
Possible Duplicate:
What is the !! operator in JavaScript?
What does !! (double exclamation point) mean?
I am going through some custom JavaScript code at my workplace and I am not able to understand the following construct.
我正在我的工作场所浏览一些自定义 JavaScript 代码，但我无法理解以下结构。
var myThemeKey = (!!$('row') && $('row').hasClassName('green-theme')) ? 'green' : 'white';
I understand everything on the above line except !!operator. I assume that it is a NOToperator and NOTof NOTis the original value but why would someone do a NOTof NOT?
除了!!操作符，我理解上面一行的所有内容。我假设它是一个NOT运算符，而NOTofNOT是原始值，但为什么有人会做 a NOTof NOT？
Can someone please help me understand what is happening on the above line of code?
有人可以帮我理解上面的代码行发生了什么吗？
回答by i_am_jorf
The !!ensures the resulting type is a boolean (true or false).
在!!确保得到的类型是布尔型（真或假）。
javascript:alert("foo")--> foo
javascript:alert("foo")--> foo
javascript:alert(!"foo")--> false
javascript:alert(!"foo")--> false
javascript:alert(!!"foo")--> true
javascript:alert(!!"foo")--> true
javascript:alert(!!null)--> false
javascript:alert(!!null)--> false
They do this to make sure $('row')isn't null.
他们这样做是为了确保$('row')不为空。
It's shorter to type than $('row') != null ? true : false.
输入比$('row') != null ? true : false.
