Javascript重新定义了Infinity，NaN或“".为0 [英] Javascript redefine Infinity, NaN, or "" as 0

问题描述

我有一个JavaScript计算器，可以接受用户输入，进行一些数学运算并将结果写入输入字段"#theResult"

I have a javascript calculator which accepts user input, does some math and writes the result to the input field "#theResult"

由于"#theResult"在键盘上更新，因此有时"#theResult"将返回Infinity，NaN或"，直到填写完所有字段.在填写所有字段之前，我希望"#theResult"返回0.这是代码:

Since "#theResult" updates on keyup, there are times when "#theResult" will return Infinity, NaN, or "" until all of the fields are filled out. Until all of the fields are filled out, I want "#theResult" to return 0 instead. Here is the code:

if (theResult === Infinity || theResult === "" || theResult === NaN) {
    theResult === 0;
}
$("#theResult").val(theResult);

完整代码为此处

在此先感谢您的帮助！

推荐答案

您已使用theResult === 0，而应使用theResult = 0.

===用于比较.如果要更改变量的值，请使用赋值运算符=.

The === is for comparisons. When you want to change the value of a variable, you use the assignment operator =.

就像@zzzzBov所说的那样，最简单的方法是将整个内容替换为

Like @zzzzBov said, the simplest thing to do is replace the whole thing with

 theResult = isFinite(theResult) && theResult || 0; // updated

这掩盖了NaN的微妙之处；如果用户完成操作并且结果确实是NaN，则表明0并不正确.

That glosses over the subtleties of NaN however; if the user is finished and the result really is NaN, showing that as 0 is not really correct.

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