Javascript regexp 字面量和构造函数之间的差异 [英] Differences between Javascript regexp literal and constructor

问题描述

我们最近遇到了一个错误，在一位开发人员将 RegExp 文字更改为构造函数调用之后，我想知道为什么会有任何区别.确切的代码是

var parts = new RegExp("/rt:([^@]+)@(d+)/").exec(tag);

对比原版

var parts =/rt:([^@]+)@(d+)/.exec(tag);

当 tag 为例如 rt:60C1C036-42FA-4073-B10B-1969BD2358FB@00000000077 时，第一个(有问题的)调用返回 null，而第二个返回<代码>["rt:60C1C036-42FA-4073-B10B-1969BD2358FB@00000000077", "60C1C036-42FA-4073-B10B-1969BD230007">

不用说，我恢复了更改，但我想知道为什么首先会有如此大的差异.

解决方案

有两个问题:

/ 是表达式的不是的一部分.它们是分隔符，标记一个正则表达式文字.如果您使用 RegExp，则必须删除它们，否则它们会按字面意思匹配斜杠.

其次，反斜杠是字符串文字中的转义字符.要为表达式创建文字 ，您必须在字符串中对其进行转义.

因此，相当于:

new RegExp("rt:([^@]+)@(\d+)")

<小时>

特别是如果您想使用 RegExp，转义会使表达式更难编写.实际上只有当你想动态创建表达式时才需要它，也就是说，如果你想包含存储在变量中的文本.如果你有一个固定的表达式，文字 /.../ 更容易写，更简洁.

We recently had a bug, after a fellow developer changed a RegExp literal into a constructor call, and I was wondering why there is any difference at all. The exact code was

var parts = new RegExp("/rt:([^@]+)@(d+)/").exec(tag);

vs the original of

var parts = /rt:([^@]+)@(d+)/.exec(tag);

When tag is, for example rt:60C1C036-42FA-4073-B10B-1969BD2358FB@00000000077, the first (buggy) call returns null, while the second one returns["rt:60C1C036-42FA-4073-B10B-1969BD2358FB@00000000077", "60C1C036-42FA-4073-B10B-1969BD2358FB", "00000000077"]

Needless to say, I reverted the change, but I'd like to know why is there such a difference in the first place.

解决方案

There are two problems:

The / are not part of the expression. They are delimiters, marking a regex literal. They have to be removed if you use RegExp, otherwise they match a slash literally.

Secondly, the backslash is the escape character in string literals. To create a literal for the expression, you have to escape it in the string.

Thus, the equivalent would be:

new RegExp("rt:([^@]+)@(\d+)")

---

Especially the escaping makes expression a bit more difficult to write if you want to use RegExp. It is actually only needed if you want to create expression dynamically, that is, if you want to include text stored in a variable for example. If you have a fixed expression, a literal /.../ is easier to write and more concise.

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