JSFiddle - React, Tailwind, and code Playground

HTML

<form action="" method="post">
    <label for="name">Name: <span id="errorMsgName"></span></label>
    <input type="text" name="name" id="name" />
    <label for="mail">E-Mail: <span id="errorMsgMail"></span></label>
    <input type="text" name="mail" id="mail" />
    <label for="text">Text: <span id="errorMsgText"></span></label>
    <textarea name="text" id="text"></textarea>
    <input type="submit" value="Senden" onclick="return checkInput()" />
  </form>

JavaScript

function checkInput(){
    var ret = true;
    var name = document.getElementById("name");
    var mail = document.getElementById("mail");
    var text = document.getElementById("text");

    // prüfe namen
    if(name.value == "") {
      document.getElementById("errorMsgName").innerText = "Bitte ausfüllen";
      ret = false;
    } else {
      document.getElementById("errorMsgName").innerText = "";
    }

    // prüfe mail
    if(mail.value == "") {
      document.getElementById("errorMsgMail").innerText = "Bitte ausfüllen";
      ret = false;
    } else {
      document.getElementById("errorMsgMail").innerText = "";
    }

   // prüfe text
    if(text.value == "") {
      document.getElementById("errorMsgText").innerText = "Bitte ausfüllen";
      ret = false;
    } else {
      document.getElementById("errorMsgText").innerText = "";
    }

    return ret;
  }