javascript 在javascript中将字符串转换为数字
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convert string to a number in javascript
提问by Om3ga
I want to parse a user input which contains longitude and latitude. What I want to do is to coerce a string to a number, preserving its sign and decimal places. But what I want to do is to display a message when user's input is invalid. Which one should I follow
我想解析包含经度和纬度的用户输入。我想要做的是将字符串强制为数字，保留其符号和小数位。但是我想要做的是在用户输入无效时显示一条消息。我应该关注哪一个
parseFloat(x)
second
第二
new Number(x)
third
第三
~~x
fourth
第四
+x
回答by Pointy
I'd use Number(x), if I had to choose between those two, because it won't allow trailing garbage. (Well, it "allows" it, but the result is a NaN.)
Number(x)如果必须在这两者之间进行选择，我会使用，因为它不允许尾随垃圾。（好吧，它“允许”它，但结果是NaN.）
That is, Number("123.45balloon")is NaN, but parseFloat("123.45balloon")is 123.45(as a number).
也就是说，Number("123.45balloon")是NaN，但是parseFloat("123.45balloon")是123.45（作为一个数字）。
As Mr. Kling points out, which of those is "better" is up to you.
正如克林先生指出的那样，哪些“更好”取决于您。
edit— ah, you've added back +xand ~~x. As I wrote in a comment, +xis equivalent to using the Number()constructor, but I think it's a little risky because of the syntactic flexibility of the +operator. That is, it'd be easy for a cut-and-paste to introduce an error. The ~~xform is good if you know you want an integer (a 32-bit integer) anyway. For lat/long that's probably not what you want however.
编辑- 啊，你又加回来了+x和~~x。正如我在评论中写的，+x相当于使用Number()构造函数，但我认为由于+操作符的语法灵活性，它有点冒险。也就是说，剪切和粘贴很容易引入错误。~~x如果你知道你想要一个整数（一个 32 位整数），那么这个形式就很好。然而，对于经纬度，这可能不是您想要的。
回答by Ates Goral
The first one is better. It is explicit, and it is correct. You said you want to parse floating point numbers. ~~xwill give you an integer.
第一个更好。这是明确的，也是正确的。你说你想解析浮点数。~~x会给你一个整数。
回答by Engineer
To test whether inputis number, use this:
要测试是否input为数字，请使用以下命令：
function isNumeric(obj){
return !isNaN( parseFloat(obj) ) && isFinite( obj );
}
To cast Stringto Number, use +,it's the fastest method:
要强制转换String为Number，使用+，这是最快的方法：
the unary + operator also type-converts its operand to a number and because it does not do any additional mathematical operations it is the fastest method for type-converting a string into a number
一元 + 运算符还将其操作数类型转换为数字，并且由于它不执行任何额外的数学运算，因此它是将字符串类型转换为数字的最快方法
So overall, probably you need this:
所以总的来说，可能你需要这个：
if(!isNumeric(inputValue)){
alert('invalid number');
}else{
var num = +inputValue;
}
isNumericborrowed from jQuery
isNumeric借来的 jQuery
回答by M. Ahmad Zafar
This is the code I would write to repeatedly take input until the correct one is obtained.
这是我将编写的代码以重复输入，直到获得正确的输入。
var d;
do {
d = prompt("Enter a number");
d = new Number(d);
} while( isNaN(d) );
document.write( d );
Note:new Number(d)will always give NaNif any character is non-numeric while parseFloat(d)will ignore trailing invalid characters.
注意：如果任何字符是非数字，new Number(d)将始终给出NaN，而parseFloat(d)将忽略尾随无效字符。
