Add commas or spaces to group every three digits

Question

I have a function to add commas to numbers:

function commafy( num ) {   num.toString().replace( /\B(?=(?:\d{3})+)$/g, "," ); } 

Unfortunately, it doesn't like decimals very well. Given the following usage examples, what is the best way to extend my function?

commafy( "123" )                 // "123" commafy( "1234" )                // "1234"                                  // Don't add commas until 5 integer digits commafy( "12345" )               // "12,345" commafy( "1234567" )             // "1,234,567" commafy( "12345.2" )             // "12,345.2" commafy( "12345.6789" )          // "12,345.6789"                                  // Again, nothing until 5 commafy( ".123456" )             // ".123 456"                                  // Group with spaces (no leading digit) commafy( "12345.6789012345678" ) // "12,345.678 901 234 567 8" 

Presumably the easiest way is to first split on the decimal point (if there is one). Where best to go from there?

Answer 1

Just split into two parts with '.' and format them individually.

function commafy( num ) {     var str = num.toString().split('.');     if (str[0].length >= 5) {         str[0] = str[0].replace(/(\d)(?=(\d{3})+$)/g, '$1,');     }     if (str[1] && str[1].length >= 5) {         str[1] = str[1].replace(/(\d{3})/g, '$1 ');     }     return str.join('.'); }