How to Match Multiline Content with JavaScript Regular Expressions?

Overcoming JavaScript Regex Boundaries for Multiline Matches

When working with JavaScript regular expressions, it becomes crucial to understand how to match content that spans multiple lines. Consider the following code snippet attempting to extract a PRE block with newlines within it:

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

ddd"; var arr = ss.match(//gm); alert(arr); // null</code>

The expected outcome is to capture the entire PRE block, but the result is a null alert. To rectify this, we delve into the intricacies of multiline matching.

The '.|[rn]' Gambit

An initial approach involves replacing the . wildcard character with an expression that matches any character or line break: (.|[rn]). However, this proves ineffective.

The Revelation: [sS]

The key to success lies in using [sS] instead of . for multiline matching. This character class encompasses both whitespace and non-whitespace characters, effectively addressing the issue.

<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">...<\/pre></code>

The Subtleties of Greed: '?' vs. ''

Another consideration relates to the quantifier used. While might seem like the obvious choice, it introduces unnecessary greediness. '?' or ' ?' ensures that the match finds the first occurrence instead of the longest possible one.

A Note on [^]

While [^] can also serve as a multiline dot, it is deprecated as per a comment in another post. Therefore, it's better to stick with [sS].

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