parseInt vs unary plus - 何时使用哪个 [英] parseInt vs unary plus - when to use which

问题描述

这一行之间有什么区别：

What are the differences between this line:

var a = parseInt("1", 10); // a === 1

此行

var a = +"1"; // a === 1

这 jsperf test 显示一元运算符在当前chrome版本中要快得多，假设它是针对node.js的！？

This jsperf test shows that the unary operator is much faster in the current chrome version, assuming it is for node.js!?

如果我尝试转换不是数字的字符串，则返回 NaN ：

If I try to convert strings which are not numbers both return NaN:

var b = parseInt("test" 10); // b === NaN
var b = +"test"; // b === NaN

所以我应该何时使用 parseInt 超过一元加（特别是在node.js中）???

So when should I prefer using parseInt over the unary plus (especially in node.js)???

编辑：和有什么不同双波浪形运算符 ~~ ？

edit: and what's the difference to the double tilde operator ~~?

推荐答案

请参阅这个答案了解更完整的案例

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嗯，这里有一些我所知道的差异：

Please see this answer for a more complete set of cases

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Well, here are a few differences I know of:

• 空字符串评估为 0 ，而 parseInt 将其评估为 NaN 。 IMO，一个空白字符串应该是 NaN 。

• An empty string "" evaluates to a 0, while parseInt evaluates it to NaN. IMO, a blank string should be a NaN.

+'' === 0;              //true
isNaN(parseInt('',10)); //true

一元 + 更像 parseFloat ，因为它也接受小数。

The unary + acts more like parseFloat since it also accepts decimals.

parseInt 另一方面当它看到非数字字符时会停止解析，例如预期的时间段小数点。。

parseInt on the other hand stops parsing when it sees a non-numerical character, like the period that is intended to be a decimal point ..

+'2.3' === 2.3;           //true
parseInt('2.3',10) === 2; //true

parseInt 和 parseFloat 从左到右解析并构建字符串 。如果他们看到无效字符，则返回已解析的内容（如果有）作为数字，如果没有解析为数字，则返回 NaN 。

parseInt and parseFloat parses and builds the string left to right. If they see an invalid character, it returns what has been parsed (if any) as a number, and NaN if none was parsed as a number.

另一方面，一元 + 将返回 NaN 如果整个字符串不可转换为数字。

The unary + on the other hand will return NaN if the entire string is non-convertible to a number.

parseInt('2a',10) === 2; //true
parseFloat('2a') === 2;  //true
isNan(+'2a');            //true

如@Alex K. ， parseInt 和 parseFloat 将按解析字符。这意味着十六进制和指数表示法将失败，因为 x 和 e 被视为非数字组件（至少在base10）。

As seen in the comment of @Alex K., parseInt and parseFloat will parse by character. This means hex and exponent notations will fail since the x and e are treated as non-numerical components (at least on base10).

一元 + 会正确转换它们。

parseInt('2e3',10) === 2;  //true. This is supposed to be 2000
+'2e3' === 2000;           //true. This one's correct.

parseInt("0xf", 10) === 0; //true. This is supposed to be 15
+'0xf' === 15;             //true. This one's correct.

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