使用ajax调用php函数

Question

I have a editor embeded in the html page

<div id="editor">
Problem Statement goes here&hellip;
</div>

I basically want to store the contents written in editor to a file(preferably in rich text format). I used a script (given below) for storing the contents in a string.(This I used by referring to HTML div text to save and display )

<script type='text/javascript' src="http://ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js"> 
     var StoreEditorContent;  //declare a variable to save Content

      document.getElementById('save').addEventListener("click", SaveText);  // adding event listner for onclick for Saving text

    function SaveText(){

       StoreEditorContent = document.getElementById('editor').innerHTML; // Save the Content into 
       document.getElementById('editor').innerHTML = ""; // to blank the editor Content
       window.onload = function(){

                $.ajax({
                    url: "submit_request.php",
                    type: "GET",
                    success: function writeMsg(StoreEditorContent){
                       //Not sure if this part is right.
                    }
                });   
        }
    }

    </script>

This of course is storing in the contents in a string StoreEditorContent. I now want to pass this string to a php function which will write this(StoreEditorContent) to a file.The php file that contains function to write is given below

<?php

function writeMsg($msg){
    $file = "myfile.txt";
    file_put_contents($file, $msg);
}
?>

I know I need to use ajax here, but cannot figure out how? Any help appreciated.