How to Effectively Match Multiline Text with Regular Expressions in JavaScript?

Overcoming Multiline Regex Pitfalls in JavaScript

When attempting to match multiline text using regular expressions in JavaScript, it is crucial to address a common pitfall. The 'm' flag, intended for multiline mode, surprisingly fails to handle newlines within the pattern. To effectively extract text across multiple lines, an alternative approach is required.

Solution: Employing [sS] for Multiline Matching

The solution lies in utilizing [sS] instead of the conventional . for multiline matching. [sS] represents any character, including whitespaces and newlines, effectively capturing text spanning multiple lines. This is illustrated in the following code:

<code class="js">var ss = "<pre class="brush:php;toolbar:false">aaaa\nbbb\nccc

ddd"; var arr = ss.match(//gm); alert(arr); // <pre class="brush:php;toolbar:false">...</u>pre> :)</code>

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Alternative Approaches

While using [sS] is a reliable solution, there are alternative approaches worth considering. Some developers recommend using [^], but it is deprecated and may not be supported in all browsers. Others suggest employing (.|[rn]), but it is significantly slower compared to [sS], as demonstrated in the provided benchmark:

Using [^]: fastest
Using [\s\S]: 0.83% slower
Using (.|\r|\n): 96% slower
Using (.|[\r\n]): 96% slower

Avoidance of Greediness

In addition to using [sS], it is advisable to avoid greediness in quantifiers. Where necessary, employ ? or ? instead of or , as this can significantly impact performance.

By leveraging these techniques, developers can overcome the challenge of multiline regex matching in JavaScript, ensuring accurate and efficient extraction of text across multiple lines.

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