Split string every 3 characters from back using JavaScript

Question

How do we split a string every 3 characters from the back using JavaScript?

Say, I have this:

str = 9139328238

after the desired function, it would become:

parts = ['9','139','328','238']

How do we do this elegantly?

Answer 1

I know this is an old question, but I would like to provide my own one-line version to solve the problem :)

"12345678".split('').reverse().join('').match(/.{1,3}/g).map(function(x){
    return x.split('').reverse().join('')
}).reverse()

This basically reverses the string, captures the groups of 3 elements, reverses each group and then reverses the whole string.

The steps are:

"12345678" -> [1, 2, 3, 4, 5, 6, 7, 8] //.split('')
[1, 2, 3, 4, 5, 6, 7, 8] -> [8, 7, 6, 5, 4, 3, 2, 1] //.reverse()
[8, 7, 6, 5, 4, 3, 2, 1] -> "87654321" //.join('')
"87654321" -> [876, 543, 21] //.match(...)
[876, 543, 21] -> [678, 345, 12] //.map(function(x){...})
[678, 345, 12] -> [12, 345, 678] //.reverse()

You can then join the array with a character (e.g. the ',' for thousands separator)

[12, 345, 678].join(',') -> "12,345,678"

Answer 2

var myString = String( 9139328238 );
console.log( myString.split( /(?=(?:...)*$)/ ) );
// ["9", "139", "328", "238"]

I can't make any performance guarantees. For smallish strings it should be fine.

Here's a loop implementation:

function funkyStringSplit( s )
{
    var i = s.length % 3;
    var parts = i ? [ s.substr( 0, i ) ] : [];
    for( ; i < s.length ; i += 3 )
    {
        parts.push( s.substr( i, 3 ) );
    }
    return parts;
}

Answer 3

There are a lot of complicated answers here.

function group(value) {
  return value.match(/\d{1,3}(?=(\d{3})*$)/g);
}

console.log(group('1'));
console.log(group('123'));
console.log(group('1234'));
console.log(group('12345'));
console.log(group('123456'));
console.log(group('1234567'));
console.log(group('12345678'));
console.log(group('123456789'));