Mastering the Browser’s Back Button with JavaScript Techniques

A common challenge that arises when developing with JavaScript is preserving the functionality of the browser’s Back button. When your page dynamically updates content using JavaScript instead of fetching a new page from the server, no new history entry is created. As a result, users pressing the Back button might be taken to the last website they visited instead of the previous state of the application they are currently using.

Interactive features like drag and drop enhance the user experience on web applications. However, if after navigating your application a user’s click on the Back button sends them back to their Start screen instead of a previous state, it can be frustrating. In this guide, we’ll explore how Rob Crowther, author of “Hello! HTML5 & CSS3,” demonstrates utilizing the HTML5 history API to prevent this kind of issue.

Consider a basic scenario. You have a function that updates the page content based on user actions:

var numberOfClicks = 0;
function handleClick() {
 numberOfClicks++;
 document.getElementById('clickDisplay').innerHTML =
 'You've clicked <b>' + numberOfClicks + '</b> times';
}

Accompanied by the following HTML elements:

<div onclick="handleClick();">Try it Out!</div>
<div id="clickDisplay">You've clicked <b>0</b> times</div>

In practice, your web page might be pulling fresh content via AJAX or another method. For demonstration purposes, even a simple on-page update can illustrate the issue. Imagine what happens next after the user interacts with the application:

1. The user leaves their homepage to check out the new Click Me feature they’ve heard about.
2. They navigate to the Click Me page directly via URL or through a link.
3. After interacting briefly with the page, several state changes occur due to their actions.
4. Once they decide to go back by pressing the Back button, they’re unexpectedly taken straight to their homepage.

To rectify this, the handleClick() function can be revised to engage with the history API. With each update, the location.hash is also modified:

function handleClick() {
 numberOfClicks++;
 location.hash = 'click' + numberOfClicks;
 document.getElementById('clickDisplay').innerHTML =
 'You've clicked <b>' + numberOfClicks + '</b> times';
}

1. The user lands on the Click Me page as they did previously.
2. The URL now updates with each click, including a new hash value.
3. Upon clicking Back, the URL changes back to ‘#click2’, signifying that the page states are now captured in the browser history. However, this doesn’t automatically restore the previous page state.

Synchronizing the Page with the Browser History

Altering the browser history is only one aspect of the equation. The other critical part is ensuring your page state aligns with the history state. To synchronize the page state with changes to location.hash, you can listen for the hashchange event:

function handleClick() {
 numberOfClicks++;
 location.hash = 'click' + numberOfClicks;
}
window.onhashchange = function() { 
 if (location.hash.length > 0) { 
 numberOfClicks = parseInt(location.hash.split('click')[1], 10); 
 } else {
 numberOfClicks = 0;
 }
 document.getElementById('clickDisplay').innerHTML = 
 'You've clicked <b>' + numberOfClicks + '</b> times';
}

Now, handleClick() is solely tasked with updating the click counter and hash. The onhashchange event belongs to the window object and is triggered by hash changes. In this instance, you ensure that the hash has content and is valid. The value of numberOfClicks is then set according to the hash’s number, and the page content is refreshed to reflect the updated state. Let’s examine how the new implementation behaves:

1. The URL’s hash is modified with each user click like before.
2. However, when the Back button is used now, the onhashchange function activates, resetting the page state in line with the URL’s hash.

Utilizing location.hash for View Navigation

location.hash and hashchange events are quite handy for marking specific views in your application and enabling users to navigate between them. An example of this is Gmail, which lets you switch between views like your inbox (#inbox) and contacts (#contacts) with the URL changing as you move and then use the Back button. You can observe this behavior by checking your Gmail account.

Nevertheless, when it comes to representing state data, the hash can only hold a string. While it’s possible to encode a complex object within the hash, the resulting URL can become lengthy and confusing. For a more sophisticated approach, you might consider using the hash as a reference to pull comprehensive state data from a storage source. HTML5 simplifies this process with history.pushState() and the popstate event, which allow you to save and read complex state objects.

Final Thoughts

By mastering browser history management techniques, you can ensure the Back button operates logically within the context of your application, providing a smoother user experience. Alongside this, the microdata API gives you access to structured semantic data within page content.

What are your thoughts on these strategies? Do you employ alternative methods? Share your insights below.