send-whatsapp-msg.js

function dispatch(target, eventType, char) {
   var evt = document.createEvent("TextEvent");    
   evt.initTextEvent (eventType, true, true, window, char, 0, "en-US");
   target.focus();
   target.dispatchEvent(evt);
}


dispatch(document.querySelector("#compose-input div"), "textInput", "hello!");

function triggerClick() {
  var event = new MouseEvent('click', {
    'view': window,
    'bubbles': true,
    'cancelable': true
  });
  document.querySelector(".icon.btn-icon.icon-send").dispatchEvent(event)
}
triggerClick()