JSFiddle - React, Tailwind, and code Playground

HTML

<textarea id="fld_8212735_1"></textarea>
<span id="maxChars">2000</span> Zeichen verfĂĽgbar

JavaScript

let textarea = document.getElementById("fld_8212735_1");
      textarea.setAttribute("maxlength", 2000);
      
      let allowedChars = 2000;
      let filledCharsBefore = 0;
      let filledChars = 0;
  
      textarea.addEventListener("keyup", function(ev){
          
          if(ev.code == "Backspace" || ev.code == "Delete" || ev.code == "NumpadDecimal"){
                filledChars = textarea.value.length;
          
              allowedChars = 2000 - filledChars ;
        }else{
            if(filledChars < 1 ){
                filledChars = textarea.value.length;         
            }else if(filledChars >= 1){
                filledChars = textarea.value.length;
                filledCharsBefore = filledChars - 1;
            }
          
              allowedChars = allowedChars - (filledChars - filledCharsBefore) ;
        }
          
          document.getElementById("maxChars").innerText = allowedChars;
    });