Why Does JavaScript Regex Fail to Extract Multiline Text with the 'm' Flag?

Regex Dilemma: Multiline Text Extraction

In an attempt to extract text from HTML using JavaScript regex, a developer encountered an unexpected obstacle: the multiline flag (m) seemed ineffective in capturing multiline text.

The provided regex pattern aimed to extract the text enclosed within an h1 tag:

var pattern = /<div>

However, when the HTML string contained newlines (n), the result consistently came up empty. Removing the newlines resolved the issue, regardless of whether the m flag was present.

The Solution: Dotall Modifier

The culprit lay in the lack of a dotall modifier in JavaScript. By default, the dot (.) matches any character except newline. To overcome this limitation, a workaround involving character classes and their negation can be employed:

[\s\S]

This character class matches any character, including newlines and other whitespace. Incorporated into the regex, it yields:

/<div>

Modern Solution with DotAll Flag

As of ES2018, JavaScript supports the s (dotAll) flag. This flag explicitly instructs the regex engine to allow the dot to match newlines, eliminating the need for workarounds:

/<div>

The above is the detailed content of Why Does JavaScript Regex Fail to Extract Multiline Text with the 'm' Flag?. For more information, please follow other related articles on the PHP Chinese website!