I have this:

1231231234

I wish to insert a space every 3 - 4 characters, so it's formatted like so:

123 123 1234

Is this possible with regex? I have something that enters a space every 3 characters but I am unsure how to do a mix of 3 and 4 characters to get the above format.

value.replace(/\B(?=(\d{3})+(?!\d))/g, " ");

I have this:

1231231234

I wish to insert a space every 3 - 4 characters, so it's formatted like so:

123 123 1234

Is this possible with regex? I have something that enters a space every 3 characters but I am unsure how to do a mix of 3 and 4 characters to get the above format.

value.replace(/\B(?=(\d{3})+(?!\d))/g, " ");

• javascript

• 2 When 3 and when 4? – sagi Commented Oct 2, 2018 at 13:19
• It's in the example above. – panthro Commented Oct 2, 2018 at 13:29
• So every string is made of the numbers 1, 2, 3, and 4? And it's either 123 or 1234? – Andy Commented Oct 2, 2018 at 13:32
• Do you always have a 10 characters string without spaces? Just use slice or substring. Using a regex is pointless here. – plalx Commented Oct 2, 2018 at 13:35

3 Answers 3

You can use a regex with lookahead.

The Positive Lookahead looks for the pattern after the equal sign, but does not include it in the match.

function format(s) {
    return s.toString().replace(/\d{3,4}?(?=...)/g, '$& ');
}

console.log(format(1234567890));
console.log(format(123456789));
console.log(format(1234567));
console.log(format(123456));
console.log(format(1234));
console.log(format(123));

value = "1231231234";

console.log(value.replace(/^(.{3})(.{3})(.*)$/, "$1 $2 $3"));

// add spaces after every 4 digits (make sure there's no trailing whitespace)
somestring.replace(/(\d{4})/g, '$1 ').replace(/(^\s+|\s+$)/,'')