Javascript RegEx to replace white space between two specific expressions

Question

I'm trying to remove space character from a string only when it is bewteen a number and the G letter.

Sample text: XXX YYY AAA 16Gb 16 Gb 16 G 2 G ZZZ

Target result: XXX YYY AAA 16Gb 16Gb 16G 2G ZZZ

What I have so far is:

'XXX YYY AAA 16Gb 16 Gb 16 G 2 G ZZZ'.replace(/\d+ gb?/ig, '?')

Answer 1

You could capture a digit and a space (or 1+ spaces) and assert the G at the right.

In the replacement use group 1 $1 and enable the /g flag to replace all occurrences and possibly /i for a case insensitive match.

(\d) +(?=G)

• (\d) Capture a single digits
• + Match 1+ spaces
• (?=G) Positive lookahead, assert a G char to the right

Regex demo

 const regex = /(\d) +(?=G)/g; console.log("XXX YYY AAA 16Gb 16 Gb 16 G 2 G ZZZ".replace(regex, "$1"));

Answer 2

In new version of JS we have look-ahead and look-behind assertion which means you can do:

"XXX YYY AAA 16Gb 16 Gb 16 G 2 G ZZZ".replace( /(?<=\d) +(?=G)/g, "" )

and outputs:

"XXX YYY AAA 16Gb 16Gb 16G 2G ZZZ"

which says (?<=\d) +(?=G) :

• (?<=\d) look-behind to find a single number but do include it in the match
• + match one or more space(s)
• (?=G) look-ahead to find G but do not include it in the match

More

• Lookahead and lookbehind in modern JS
• Why are lookbehind assertions not supported in Javascript?
• Here you can also see the support for lookbehind thanks to @Thefourthbird

Answer 3

You can achieve this easily by creating Regex groups. Notice the () surrounding both the digit and the "g" and then reusing them in the replace function by indexing them.

console.log("XXX YYY AAA 16Gb 16 Gb 16 G 2 G ZZZ".replace(/([\d])\s*(g)/ig, '$1$2'))