Coding Challenge Practice - Question 104

The task is to create a function that adds commas as thousand separators.

The boilerplate code

function addComma(num) {
  // your code here
}

Convert the number to string. Strings are easier to manipulate digit by digit. Then, split integer and decimal parts. Numbers after decimals don't require commas

const [integer, decimal] = String(num).split(".");

Handle negative integers

const sign = integer.startsWith("-") ? "-" : "";
const digits = sign ? integer.slice(1) : integer;

If the number is negative, the minus sign is saved in signand removed temporarily from digits.

Prepare variables for building the result

let result = ""
let count = 0

result is used to build the final string. Count counts the number of digits since the last comma. Add a comma after every 3 digits

  for (let i = digits.length - 1; i >= 0; i--) {
    result = digits[i] + result;
    count++;

    if (count % 3 === 0 && i !== 0) {
      result = "," + result;
    }
  }

Add the sign and decimal afterwards

return sign + result + (decimal ? "." + decimal : "");

The final code

function addComma(num) {
  // your code here
  const[integer, decimal] = String(num).split(".");
  const sign = integer.startsWith("-") ? "-" : "";
  const digits = sign ? integer.slice(1) : integer;

  let result = "";
  let count = 0;

  for(let i = digits.length -1; i >= 0; i--) {
    result = digits[i] + result;
    count++;

    if(count % 3 === 0 && i !== 0) {
      result = "," + result
    }
  }
  return sign + result + (decimal ? "." + decimal : "")
}

That's all folks!