Add a millennial sign to a number (amount in millennia)

Method 1 （ Can be signed and decimal ）

//  Add a thousand separator to the number 
export function addThousandSplit(num) {
    
  let flag = false;
  num = num + '';
  let firstStr = num.slice(0, 1);
  if(firstStr === '+' || firstStr === '-') {
    
    num = num.slice(1);
    flag = true;
  }
  let integer = num.split('.')[0];
  let surplus = num.split('.')[1];
  const arr = integer.split('');
  const val = arr.reduceRight((acc, cur, index) => {
    
    if ((arr.length - 1 - index) % 3 === 2 && index !== 0) {
    
      cur = ',' + cur;
    }
    return cur + acc;
  }, '');
  if(flag === true) {
    
    flag = false;
    return surplus ? firstStr + val + '.' + surplus : firstStr + val;
  } else {
    
    return surplus ? val + '.' + surplus : val;
  }
}

Method 2

// Kilogram format method （ whole number with a decimal ）
export function formatNumber(val) {
    
  let value = val + '';
  console.log(value);
  if(value.indexOf('.') !== -1) {
    
    let intPart = value.slice(0, value.indexOf('.'));
    let floatPart = value.slice(value.indexOf('.') + 1);
    let formatIntPart = Number(intPart).toLocaleString('en-US');
    let result = formatIntPart + '.' + floatPart;
    return result;
  } else {
    
    return Number(value).toLocaleString('en-US');
  }
}

Method 3

value.toLocaleString('en-US');

** Be careful ： Here's a request value Must be number type .

Remove the thousandth

// Kilogram format method （ whole number with a decimal ）
DelThousandSplit(val) {
    
   let value = val + '';
   if(value.indexOf('.') !== -1) {
    
     let intPart = value.slice(0, value.indexOf('.'));
     let floatPart = value.slice(value.indexOf('.') + 1);
     let formatIntPart = intPart.split(',').join('');
     let result = formatIntPart + '.' + floatPart;
     return result;
   } else {
    
     return value.split(',').join('');
   }
 }