How Can I Persist Variables Across Page Reloads in Web Applications?

How to Persist Variables Between Page Loads

Keeping track of user actions across page reloads is crucial for enhancing user experience in web applications. However, due to the stateless nature of HTTP, this task can be challenging.

Attempt and Error

An unsuccessful attempt to capture the form submit event and subsequently unhide hidden fields was reported. The JavaScript code employed a global variable (clicked) to store the submit status, but it failed to persist its value upon page refresh.

Solutions

To overcome this issue, there are several methods that can be implemented:

1. Query String

When submitting forms using the GET method, the URL updates with a query string containing parameter-value pairs. This allows you to set an input field in the form to a specific value. For example, a hidden field can be added:

<form method="GET">
<input type="hidden" name="clicked" value="true" />
<input type="submit" />
</form>

On subsequent page loads, you can use JavaScript to parse the query string and check for any passed values:

function getParameterByName(name) {
    name = name.replace(/[\[]/, "\[").replace(/[\]]/, "\]");
    var regex = new RegExp("[\?&]" + name + "=([^&#]*)"),
        results = regex.exec(location.search);
    return results === null ? "" : decodeURIComponent(results[1].replace(/\+/g, " "));
}

var clicked = getParameterByName('clicked');

2. Web Storage

HTML5 introduced Web Storage, which provides an API for persisting data within the browser across page loads. It offers two options: sessionStorage and localStorage.

sessionStorage:

• Data persists only during the current browsing session.
• Suitable for storing temporary data, such as clicked states.

Code to set sessionStorage on button click:

$('input[type="submit"][value="Search"]').click(function() {
    sessionStorage.setItem('clicked', 'true');
});

Code to check if sessionStorage is set on page load:

var clicked = sessionStorage.getItem('clicked');

localStorage:

• Data persists indefinitely (unless manually cleared by the user).
• Useful for storing data beyond a single browsing session.

Code to set localStorage on button click:

$('input[type="submit"][value="Search"]').click(function() {
    localStorage.setItem('clicked', 'true');
});

Code to check if localStorage is set on page load:

var clicked = localStorage.getItem('clicked');

3. Cookies

Cookies provide another mechanism for persistent data storage. Unlike Web Storage, cookies are primarily designed for server-side communication, but they can also be used for client-side data retention.

jQuery simplifies cookie handling:

$('input[type="submit"][value="Search"]').click(function() {
    $.cookie('clicked', 'true', {expires: 1}); // expires in 1 day
});

Code to read a cookie on page load:

var clicked = $.cookie('clicked');

To remove a cookie, call $.cookie('clicked', null).

4. window.name

Although somewhat unconventional, the window.name property can be used to store data across page refreshes:

window.name = "my value";

Strings or serialized objects can be stored:

window.name = JSON.stringify({ clicked: true });

However, this approach has limitations. It is accessible across tabs and domains, but only within the same browsing session. It's generally not recommended for persisting crucial data.

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