仅向用户显示一次警报

I wish to show users of my website a pop-up alert on their first visit, but not on subsequent visits.

Since I only have basic HTML and scripting knowledge, please explain how I can i implement this using cookies or other browser features.

You can see the current state of my website at http://www.hdfbcover.com/

Here is an example using cookies, you could also do something similar with localStorage rather than the cookie.

// Check If Cookie exists and if it doesn't exists
if( $.cookie('example') == null ) {
    // Create cookie
    $.cookie( 'example', '1',  { expires: 7, path: '/' } );
    // Display popup
    // Your code here...
}

Reference:

• jQuery $.cookie
• HTML5 localStorage

If you have registered users, you should decide on saving data locally or on the server:

On server

If you have a user database, you could store and set a flag (boolean value) indicating whether the user has seen the message. This could easily be made generic enough to show different kinds of messages and show them at different times. And advantage here is that you know whether the user has seen the message regardless of where he is connected from.

Locally

You could use local storage, for instance HTML5's localStorage or a jQuerys cookie plugin. There you would save flags of whether the user has seen the message. Obviously here you dont know whether the user has seen the message if he is connected from a new computer.