<input type="text" id="numebr" placeholder="NUMBER"/>
<input type="text" id="message" placeholder="MESSAGE"/>
<button onclick="send_whatsapp()">Send </button>
<script>
  function send_whatsapp(){
    var number = document.getElementById("numebr").value;
    var message = document.getElementById("message").value;
    window.open("https://api.whatsapp.com/send?phone="+number+"&text="+message);
  }
</script>