[iznoskill]

let textarea = document.getElementById('imp1');
var result = document.getElementById('result');
let count = {};
    textarea.oninput  = function (){
        let textarea = this.value;
        let length = textarea.length;
        let last_symbol = textarea.charAt(length - 1);
  
  if(count[last_symbol] === undefined){
    count[last_symbol] = 1;
        } else {
            count[last_symbol] += 1;
  }
  result.innerText = count.value;

<textarea name = "sasha" id = "imp1" cols="50" rows = "5"></textarea>
<div id = "result"></div>