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, \",\" );
}

Unfortun

Answer 1

Here are two concise ways I think maybe useful:

1. Number.prototype.toLocaleString

This method can convert a number to a string with a language-sensitive representation. It allows two parameters, which is locales & options. Those parameters may be a bit confusing, for more detail see that doc from MDN above.

In a word, you could simply use is as below:

console.log(
   Number(1234567890.12).toLocaleString()
)
// log -> "1,234,567,890.12"

If you see different with me that because we ignore both two parameters and it will return a string base on your operation system.

2. Use regex to match a string then replace to a new string.

   Why we consider this? The toLocaleString() is a bit confusing and not all browser supported, also toLocaleString() will round the decimal, so we can do it in another way.

// The steps we follow are:
// 1. Converts a number(integer) to a string.
// 2. Reverses the string.
// 3. Replace the reversed string to a new string with the Regex
// 4. Reverses the new string to get what we want.

// This method is use to reverse a string.
function reverseString(str) { 
    return str.split("").reverse().join("");  
}

/**
 * @param {string | number} 
 */
function groupDigital(num) {
  const emptyStr = '';
  const group_regex = /\d{3}/g;

  // delete extra comma by regex replace.
  const trimComma = str => str.replace(/^[,]+|[,]+$/g, emptyStr)


  const str = num + emptyStr;
  const [integer, decimal] = str.split('.')

  const conversed = reverseString(integer);

  const grouped = trimComma(reverseString(
    conversed.replace(/\d{3}/g, match => `${match},`)
  ));

  return !decimal ? grouped : `${grouped}.${decimal}`;
}


console.log(groupDigital(1234567890.1234)) // 1,234,567,890.1234
console.log(groupDigital(123456))  // 123,456
console.log(groupDigital("12.000000001"))  // 12.000000001