JS
(quick guide & examples)
<div class="remain"> USUAL TEXT AREA <textarea maxlength="160" class="txt"> </textarea>
REMAINING COUNTER <div class="count"></div> </div>
GET TEXTAREA + REMAINING COUNTER let t = document.querySelector("txt"), c = document.querySelector("count");
INIT REMAINING CHARACTERS c.innerHTML = t.maxLength;
CALCULATE REMAINING CHARACTERS t.addEventListener("keyup", () => c.innerHTML = t.maxLength - t.value.length; );