How Can I Preserve Delimiters When Splitting Strings in JavaScript Using Regular Expressions?

Preserving Delimiters When Splitting Strings in JavaScript with RegExp

Splitting a string into segments using regular expressions (RegExp) is a common task in JavaScript. However, sometimes it's desirable to preserve the delimiters used for splitting.

Consider the following string:

aaaaaa<br />&dagger; bbbb<br />&Dagger; cccc

Suppose you wish to split this string at the
delimiter, which is followed by a special character († or ‡). The following RegExp can be used:

string.split(/<br \/>&amp;#?[a-zA-Z0-9]+;/g);

While this RegExp accomplishes the splitting task, it discards the
delimiter. This can be undesirable in certain scenarios.

To retain the delimiters, various options can be employed, as demonstrated below:

string.split(/(<br \/>&amp;#?[a-zA-Z0-9]+;)/g);

By enclosing the delimiter in parentheses, the delimiters are captured as separate elements in the resulting array.

Another approach involves using a positive lookahead assertion:

string.split(/(?=<br \/>&amp;#?[a-zA-Z0-9]+;)/g);

This assertion matches the position immediately before the delimiter without actually consuming the delimiter.

Alternatively, a negative lookbehind assertion can be used:

string.split(/(?!<br \/>&amp;#?[a-zA-Z0-9]+;)/g);

This assertion matches the position immediately after the delimiter without consuming it.

Additionally, a regular expression can be used to capture the portion of the string before the delimiter:

string.split(/(.*?<br \/>&amp;#?[a-zA-Z0-9]+;)/g);

This captures everything up to the delimiter.

When dealing with paths, a special consideration is required to preserve directory slashes:

var str = 'Animation/rawr/javascript.js';
var tokens = str.match(/[^\/]+\/?|\//g);

This RegExp ensures that slashes following directories are also captured.

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