How to preserve separators in the result of String.prototype.split()

Today, I found a tiny JavaScript gem that may come in handy. You probably know the string method split().

Call it on a string, define a separator and receive an array of its substrings. Easy peasy!

"Hello party people!".split(' ');
// Array(3) [ "Hello", "party", "people!" ]

The first function parameter (the separator), can be a string value but also a regular expression. By using a regular expression you can devide the original string dependending on different separators.

// Split the string on "-" and "_"
"Hello_party-people!".split(/[-_]/);
// Array(3) [ "Hello", "party", "people!" ]

No matter if your separator is a string value or regular expression, its value is usually not included in the returned array. MDN states this functionality as follows:

But here's the JavaScript trivia: if you use a regular expression as the separator and this regular expression includes capturing parentheses (( and )), the matching values are included in the result. 😲

// Split the string on "-" and "_"
// but include the separator in the result
"Hello_party-people!".split(/([-_])/);
// Array(5) [ "Hello", "_", "party", "-", "people!" ]

I wasn't aware of this behavior, and I bet it can replace some complex regular expression logic!