问在$(文档).ready中必须声明或输入什么？

EN

alert("Without Ready");

$(document).ready(function(){
  alert("With Ready");
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

/**
Global function here, which is not called or bind on page load
*/

function alertWindow(message){
  alert ("Window is loaded here with Message: "+message);
  $("#console").text(message);
  }

$(document).ready(function(){
  
  $("#showBtn").click(function(event){
    var ourMessage = $("#message").val();
    alertWindow(ourMessage);
    });
  
  
  });

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

<input type="text" id="message" placeholder="Enter Message" >
<br>
<button id="showBtn">Show Message</button>

<p>
  <h3>Console Here</h3>
<div id="console"></div>
</p>