API Migrating legacy JavaScripts
Legacy code often contains JavaScripts that expect a full page load whenever the user interacts with the page. When you configure Unpoly to handle all interaction, there will not be additional page loads as the user clicks a link or submits a form.
This may cause some of the following issues:
- The
windowwill not emit anotherDOMContentLoadedevent when you update the page body through Unpoly. This may cause your legacy JavaScript to not run when you expect it to. - Legacy JavaScript often enhances elements on the entire page instead of scoping its changes to a region of the DOM. When we're updating fragments we only want to enhance elements within the new fragment, and don't want to touch elements that we have already enhanced.
- Legacy JavaScript may have memory leaks, e.g. by scheduling timers with
setInterval()but never clearing these timers when they're no longer needed. When you're resetting the page with every click you may never notice the leaks. However, when all links are handled through Unpoly the JavaScript VM may persist for minutes or hours and those leaks are going to stack up.
The cleanest solution to these issues is to call all your JavaScript from an Unpoly compiler.
Migrating legacy scripts to a compiler
The legacy code below waits for the page to load, then selects all links with a
.lightbox class and calls lightboxify() for each of these links:
document.addEventListener('DOMContentLoaded', function(event) {
document.querySelectorAll('a.lightbox').forEach(function(element) {
lightboxify(element)
})
})
Since the code only runs after the initial page load, links contained in a fragment update will not be "lightboxified".
You can fix this by moving your code to a compiler:
up.compiler('a.lightbox', function(element) {
lightboxify(element)
})
When the page initially loads, Unpoly will call this compiler for every element
matching a.lightbox. When a fragment is updated later, Unpoly will call this compiler
for new matches within the new fragment.
Important
Compilers should only process the given element and its children. It should not use
document.querySelectorAll()to process elements elsewhere on the page, since these may already have been compiled.
Migrating screen-specific scripts
You may sometimes have a script that enhances the HTML on the current screen:
<form action="/orders/new">
...
</form>
<script>
trackView({ screen: 'order-form', step: 1 })
</script>
To migrate this script, think of an attribute or class that should activate the behavior, and add it to the relevant element:
<form action="/orders/new" track-view"> <!-- mark: track-view -->
...
</form>
Any parameters can be attached to the element:
<form action="/orders/new" track-view up-data="{ screen: 'order-form', step: 1 }"> <!-- mark: { screen: 'order-form', step: 1 } -->
...
</form>
You can now react to an element in a compiler:
up.compiler('[track-view]', function(element, data) { // mark: [track-view]
trackView(data)
})
Running inline <script> tags
By default <script> tags will only run during the initial page load.
Scripts in updated fragments will not be loaded or executed.
If possible, migrate these scripts to a compiler.
If you absolutely want to run scripts in new fragments, you can change the default:
up.fragment.config.runScripts = true // default is false
Even with this setting, there may be reasons why a script is not executed:
- A strict Content Security Policy may forbid a script from running. See Running scripts with a CSP.
- Scripts in the
<head>are never inserted automatically. See Handling new asset versions.
Avoiding scripts in the <body>
When allowing inline scripts to run, mind that the <body> element is a default main target.
If you include your global scripts at the end of your <body>, swapping the <body> will re-execute these scripts:
<html>
<body>
<p>Content here</p>
<script src="app.js"></script> <!-- will run every time `body` is updated -->
</body>
</html>
A better solution is so move the <script> to head and give it an [defer] attribute:
<html>
<head>
<script src="app.js" defer></script> <!-- mark: defer -->
</head>
<body>
<p>Content here</p>
</body>
</html>