title: How to export html form data to json file
body: <p>How do I save html registration form data into a JSON file then log in based on it, without using any server side scripting languages? I want to use only Javascript and jQuery.</p>
  
  <p>HTML file "simple form" contains:</p>
  
  <p>First Name, Middle Name, Last Name, User Name, Password, Confirm Password, E-Mail, Phone</p>
  
  <p>When a user enters his data and clicks the register button, his data will be saved in a JSON file on the server.  I have created this JSON file on the server as:</p>
  
  <pre><code>C:\inetpub\wwwroot\usersData.txt
  </code></pre>
  
  <p>And based on this file <code>usersData.txt</code>, when another user wants to register, I need to check the that user name is unique, if it is a unique user name, save his data back to the JSON file.</p>
  
  <p>I also need to know how to update the password in the JSON file when I use a hypothetical <code>change_password()</code> JS function.</p>