Splitting a string using a JavaScript regex but keeping the delimiter? - Stack Overflow

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I'm receiving input like:

F12T213B1239T2F13T341F324

and I have to group it by letter followed by the numbers that follows it. So the ideal output would be:

F12,T213,B1239,T2,F13,T341,F324

And then do some processing on the numbers based on the letter that they're with. The letters are fixed, they are always B,F,T

So far, I've tried to split it by letter with:

var separators = ['T', 'B', 'F'];
var parts = input.split(new RegExp('('+separators.join('|')+')'),'g');

But the problem with this is that I end up with just the numbers, I need the letters with them.

Does anyone know how to split a string by certain characters but still keep the characters in the output?

I'm receiving input like:

F12T213B1239T2F13T341F324

and I have to group it by letter followed by the numbers that follows it. So the ideal output would be:

F12,T213,B1239,T2,F13,T341,F324

And then do some processing on the numbers based on the letter that they're with. The letters are fixed, they are always B,F,T

So far, I've tried to split it by letter with:

var separators = ['T', 'B', 'F'];
var parts = input.split(new RegExp('('+separators.join('|')+')'),'g');

But the problem with this is that I end up with just the numbers, I need the letters with them.

Does anyone know how to split a string by certain characters but still keep the characters in the output?

• javascript
• regex
• string

Share Improve this question Follow edited Apr 11, 2018 at 19:04 halfer 20.4k1919 gold badges109109 silver badges202202 bronze badges asked Nov 28, 2017 at 7:44 RazgrizRazgriz 7,3431717 gold badges8787 silver badges157157 bronze badges 1

• 2 Try this 'F12T213B1239T2F13T341F324'.match(/([FTB]\d*)/g) – Hassan Imam Commented Nov 28, 2017 at 7:54

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4 Answers 4

Sorted by: Reset to default 4

var str = "F12T213B1239T2F13T341F324";
var regex = /(?=T)|(?=F)|(?=B)/g;
console.log(str.split(regex));

Solution is based on Positive lookahead

One way to do this is to replace all the FTBs with a space followed by that letter:

regex: [FTB]
replacement:  $0 // note the leading space

Then, you can split it with space characters.

You can do it with a noncapturing group and some empty value filtering.

The regex is : ((?:F|T|B)\d+)

Here's a working code:

console.log(
    "F12T213B1239T2F13T341F324"
        .split(/((?:F|T|B)\d+)/g)
        .filter(d => d != "")
);

Instead of using .split() you can use .match() with a matching group in the regex, it will give you an array of all your wanted matches.

This is the regex you need /([TBF]\d{1,4})/g.

This is how should be your code:

var input = "F12T213B1239T2F13T341F324";
var separators = ['T', 'B', 'F'];
var parts = input.match(new RegExp('(['+separators.join('')+']\\d{1,4})','g'));

console.log(parts);

Note:

• The ['+separators.join('')+'] will give you the following [TBF], in your regex so it matches one of the separators.
• And \d{1,4} will match the digits following that separator.

Demo:

var input = "F12T213B1239T2F13T341F324";
var separators = ['T', 'B', 'F'];
var parts = input.match(new RegExp('(['+separators.join('')+']\\d{1,4})','g'));

console.log(parts);

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