Javascript正则表达式多行标志不起作用 [英] Javascript regex multiline flag doesn't work

问题描述

我写了一个正则表达式来从html中获取字符串，但似乎多行标志不起作用。

I wrote a regex to fetch string from html, but it seems the multiline flag doesn't work.

这是我的模式，我想得到文本在h1标签中。

this is my pattern and I want to get the text in h1 tag.

var pattern= /<div class="box-content-5">.*<h1>([^<]+?)<\/h1>/mi
m = html.search(pattern);
return m[1];

我创建了一个字符串来测试它。当字符串包含\ n时，结果始终为null。如果我删除所有\ n，它会给我正确的结果，无论是否有/ m标志。

I created a string to test it. When the string contains "\n" the result is always null. If I remove all the "\n" , it gave me the right result, no matter with or without /m flag.

我的正则表达式有什么问题？

what's wrong with my regex?

推荐答案

您正在寻找 /.../ s 修饰符，称为 dotall 修饰符。它强制点。也匹配新行，默认情况下它不执行。

You are looking for the /.../s modifier, also known as the dotall modifier. It forces the dot . to also match newlines, which it does not do by default.

坏消息是JavaScript 中不存在（从ES2018开始，见下文）。好消息是你可以通过使用字符类（例如 \s ）及其否定（ \S ），像这样：

The bad news is that it does not exist in JavaScript (it does as of ES2018, see below). The good news is that you can work around it by using a character class (e.g. \s) and its negation (\S) together, like this:

[\s\S]

因此，在您的情况下，正则表达式将成为：

So in your case the regex would become:

/<div class="box-content-5">[\s\S]*<h1>([^<]+?)<\/h1>/i

---

从ES2018开始，JavaScript支持 s （dotAll）标志，所以在现代环境中你的正则表达式可能就像你写的一样，但是带有 s 标志结束（而不是 m ; m 改变 ^ 的方式和 $ 工作，而不是。）：

---

As of ES2018, JavaScript supports the s (dotAll) flag, so in a modern environment your regular expression could be as you wrote it, but with an s flag at the end (rather than m; m changes how ^ and $ work, not .):

/<div class="box-content-5">.*<h1>([^<]+?)<\/h1>/is

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