CODEWITHSUNDEEP
javascriptregex
Don Boots
Don Boots

Reputation: 2166

javascript regex conditional number formatting

I have a task that has a few rules. Basically, I am separating a number into groups of 3. If the last group only has 1 digit in it, then the last 2 groups have 2 digits instead of 1 group of 3 and 1 group of 1.

For example:

123456789 = 123-456-789
12345678901 = 123-456-789-01
1234567 = 123-45-67

My regex so far has been:

serial.match(/\d{3}|\d+/g)

where serial is a string passed in via function

function format(serial) {
    return serial.replace('/-|/s/g', '').match(/\d{3}|\d+/g).join('-');
}

This gets me the majority of the way there, just doesn't split properly when the last match is {4}.

My progress via fiddle: https://jsfiddle.net/dboots/2mu0yp2b/2/

Upvotes: 2

Views: 101

Answers (1)

Nina Scholz
Nina Scholz

Reputation: 386519

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.

x(?=y)

Matches 'x' only if 'x' is followed by 'y'. This is called a lookahead.

For example, /Jack(?=Sprat)/ matches 'Jack' only if it is followed by 'Sprat'. /Jack(?=Sprat|Frost)/ matches 'Jack' only if it is followed by 'Sprat' or 'Frost'. However, neither 'Sprat' nor 'Frost' is part of the match results.

function format(s) {
    return s.toString().replace(/\d{2,3}(?=..)/g, '$&-');
}

document.write(format(123456789) + '<br>');
document.write(format(12345678901) + '<br>');
document.write(format(1234567) + '<br>');

Upvotes: 7

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