JSFiddle - React, Tailwind, and code Playground

HTML

<span>126913.36</span>
<span>0</span>
<span></span>
<span>0 m²</span>

CSS

span {display: block;
    margin-bottom: 10px}

JavaScript

function commaSeparateNumber(val){
    val = val.toString().replace(/,/g, ''); //remove existing commas first
    var valSplit = val.split('.'); //then separate decimals
		
    while (/(\d+)(\d{3})/.test(valSplit[0].toString())){
        valSplit[0] = valSplit[0].toString().replace(/(\d+)(\d{3})/, '$1'+','+'$2');
    }
    if(val == ""){
    val = 0 + valSplit[0] + "." + 00+ 00; 
    }
    else{
      if(valSplit.length == 2){ //if there were decimals
          val = valSplit[0] + "." + valSplit[1]; //add decimals back
      }
      if(valSplit.length == 1){
          val = valSplit[0] + "." + 00+ 00; 
      }
    }
    return val;
}

$('span').each(function(){
     var num = $(this).text();
     var txt = '0.00 m²';
     if(num == '0 m²'){
      alert("gg")
      $(this).text(txt);
     }else{
     var commaNum = commaSeparateNumber(num);
     $(this).text(commaNum);
     }
});