NavigateEvent: intercept() method
Limited availability
This feature is not Baseline because it does not work in some of the most widely-used browsers.
Experimental: This is an experimental technology
Check the Browser compatibility table carefully before using this in production.
The intercept() method of the
NavigateEvent interface intercepts this navigation, turning it into a same-document navigation to the destination URL.
Syntax
intercept()
intercept(options)
Parameters
optionsOptional-
An options object containing the following properties:
handlerOptional-
A callback function that defines what the navigation handling behavior should be; it returns a promise. This function will run after the
currentEntryproperty has been updated. precommitHandlerOptional-
A callback function that defines any behavior that should occur just before the navigation has committed; it accepts a controller object as an argument and returns a promise. This function will run before the
currentEntryproperty has been updated. focusResetOptional-
Defines the navigation's focus behavior. This may take one of the following values:
after-transition-
Once the promise returned by your handler function resolves, the browser will focus the first element with the
autofocusattribute, or the<body>element if no element hasautofocusset. This is the default value. manual-
Disable the default behavior.
scrollOptional-
Defines the navigation's scrolling behavior. This may take one of the following values:
after-transition-
Allow the browser to handle scrolling, for example by scrolling to the relevant fragment identifier if the URL contains a fragment, or restoring the scroll position to the same place as last time if the page is reloaded or a page in the history is revisited. This is the default value.
manual-
Disable the default behavior.
Return value
None (undefined).
Exceptions
InvalidStateErrorDOMException-
Thrown if the current
Documentis not yet active, or if the navigation has been cancelled. SecurityErrorDOMException-
Thrown if:
- The event was dispatched by a
dispatchEvent()call, rather than the user agent. - The navigation cannot be intercepted (
NavigateEvent.canInterceptisfalse). - A
precommitHandler()callback is provided on a non-cancelable event (Event.cancelableisfalse).
- The event was dispatched by a
Description
The intercept() method is used to implement same-document (SPA) navigation behavior when a navigation occurs; for example, when a link is clicked, a form is submitted, or a programmatic navigation is initiated (using History.pushState(), Window.location, etc.).
It does this via a couple of different callbacks, handler() and precommitHandler().
Handling immediate navigations with handler()
The handler() callback is run in response to a committed navigation. It will run after the currentEntry property has been updated, meaning that a new URL is shown in the browser UI and the history is updated with a new entry.
A typical example looks like this, enabling specific content to be rendered and loaded in response to a certain navigation:
navigation.addEventListener("navigate", (event) => {
const url = new URL(event.destination.url);
if (url.pathname.startsWith("/articles/")) {
event.intercept({
async handler() {
// Fetch the new content and display when ready
const articleContent = await getArticleContent(url.pathname);
renderArticlePage(articleContent);
},
});
}
// Include multiple conditions for different page types here, as needed
});
handler() should be used to implement navigation behavior where the navigation is committed to: the user should be shown something new.
Handling precommit actions with precommitHandler()
However, you might also wish to modify or cancel in-flight navigation, or to perform work while the navigation is ongoing and before it is committed. This kind of scenario can be dealt with using the precommitHandler() callback, which runs before the currentEntry property has been updated and the browser UI shows the new location.
For example, if the user navigates to a restricted page and is not signed in, you may want to redirect the browser to a sign-in page. This might be handled like so:
navigation.addEventListener("navigate", (event) => {
const url = new URL(event.destination.url);
if (url.pathname.startsWith("/restricted/") && !userSignedIn) {
event.intercept({
async precommitHandler(controller) {
controller.redirect("/signin/", {
state: "signin-redirect",
history: "push",
});
},
});
}
});
This pattern is simpler than the alternative of canceling the original navigation and starting a new one to the redirect location, because it avoids exposing the intermediate state. For example, only one navigatesuccess or navigateerror event fires, and if the navigation was triggered by a call to Navigation.navigate(), the promise only fulfills once the redirect destination is reached.
The precommitHandler() callback takes a controller object as an argument, which contains a redirect() method. The redirect() method takes two parameters — a string representing the URL to redirect to, and an options object containing two parameters:
stateOptional-
Contains any state information you want to pass along with the navigation; for example, for logging or tracking purposes. The state for the navigation can subsequently be retrieved via
NavigationHistoryEntry.getState(). historyOptional-
An enumerated value that specifies how this redirect should be added to the navigation history. It can take one of the following values:
auto-
The default value, which lets the browser decide how to handle it:
- If the original navigation occurred as a result of a
Navigation.navigate()call, the value will be whatever was specified in thenavigate()call'shistoryoption. - Otherwise, the value used is usually
push, but it will becomereplaceif the redirect points to the same URL as the pre-navigation URL.
- If the original navigation occurred as a result of a
push-
Adds a new
NavigationHistoryEntryto the navigation history, and clears any available forward navigation (that is, if the user previously navigated to other locations, then used the back button to return back through the history before then initiating the navigation that caused the redirect). replace-
Replaces the
Navigation.currentEntrywith theNavigationHistoryEntry.
Note:
The redirect() method can can convert the history behavior between auto, push, and replace, but it cannot turn a traverse navigation into a push/replace navigation and vice versa.
precommitHandler() generally handles any modifications to the navigation behavior that are required before the destination URL is actually displayed in the browser, cancelling or redirecting it somewhere else as required. Because precommitHandler() can be used to cancel navigations, it will only work as expected when the event's Event.cancelable property is true. Calling intercept() with a precommitHandler() on a non-cancelable event results in a SecurityError being thrown.
Responding to navigation success or failure
When the promises returned by the intercept() handler functions fulfill, the Navigation object's navigatesuccess event fires, allowing you to run cleanup code after a successful navigation has completed. If those promises reject, meaning the navigation has failed, navigateerror fires instead, allowing you to gracefully handle the failure case.
There is also a finished property on the return value of navigation methods (such as Navigation.navigate()), which fulfills or rejects at the same time as the aforementioned events are fired, providing another path for handling the success and failure cases.
Interaction between precommitHandler() and handler()
Both precommitHandler() and handler() callbacks can be included inside the same intercept() call.
-
First, the
precommitHandler()handler runs.- When the
precommitHandler()promise fulfills, the navigation commits. - If the
precommitHandler()rejects,navigateerrorfires, thecommittedandfinishedpromises reject, and the navigation is cancelled.
- When the
-
When the navigation commits, a new
NavigationHistoryEntryis created for the navigation, and itscommittedpromise fulfills. -
Next, the
handler()promise runs.- When the
handler()promise fulfills and thenavigatesuccessevent fires, the navigationfinishedpromise fulfills as well, to indicate the navigation is finished. - If
handler()rejects,navigateerrorfires, thefinishedpromise rejects, and the navigation is canceled.
- When the
Note that the above process is upheld even across multiple intercept() calls on the same NavigateEvent. All precommitHandler() callbacks are called first, and when all of them resolve, the navigation commits, and all the handler() callbacks are called.
Controlling focus behavior
By default, after a navigation handled using intercept() has occurred, the document focus will reset to the first element in the DOM with an autofocus attribute set, or otherwise to the <body> element, if no autofocus attribute is set. If you want to override this behavior, to manually implement a more accessible focus position on navigation (for example, the new top-level heading), you can do so by setting the focusReset option to manual.
navigation.addEventListener("navigate", (event) => {
const url = new URL(event.destination.url);
if (url.pathname.startsWith("/articles/")) {
event.intercept({
focusReset: manual,
async handler() {
// Fetch the new content and display when ready
const articleContent = await getArticleContent(url.pathname);
renderArticlePage(articleContent);
// Handle page focus with a custom function
setPageFocus();
},
});
}
});
Controlling scroll behavior
After an intercept() navigation occurs, the following scrolling behavior occurs:
- For
pushandreplacenavigations (seeNavigation.navigate()), the browser will attempt to scroll to the fragment given byevent.destination.url. If there is no fragment available, it will reset the scroll position to the top of the page. - For
traverseandreloadnavigations, the browser behaves similarly to the description in the previous item above in this list, but delays its scroll restoration logic until theintercept()promise fulfills. It will perform no scroll restoration if the promise rejects. If the user has scrolled during the transition then no scroll restoration will be performed.
If you want to turn this behavior off, you can do so by setting the scroll option to manual.
navigation.addEventListener("navigate", (event) => {
const url = new URL(event.destination.url);
if (url.pathname.startsWith("/articles/")) {
event.intercept({
scroll: manual,
async handler() {
// Fetch the new content and display when ready
const articleContent = await getArticleContent(url.pathname);
renderArticlePage(articleContent);
// Handle scroll behavior with a custom function
setScroll();
},
});
}
});
If you want to manually trigger the default scrolling behavior described earlier (maybe you want to reset the scroll position to the top of the page early, before the full navigation has finished), you can do so by calling NavigateEvent.scroll().
Examples
>Handling a navigation using intercept()
navigation.addEventListener("navigate", (event) => {
// Exit early if this navigation shouldn't be intercepted,
// e.g. if the navigation is cross-origin, or a download request
if (shouldNotIntercept(event)) return;
const url = new URL(event.destination.url);
if (url.pathname.startsWith("/articles/")) {
event.intercept({
async handler() {
// The URL has already changed, so show a placeholder while
// fetching the new content, such as a spinner or loading page
renderArticlePagePlaceholder();
// Fetch the new content and display when ready
const articleContent = await getArticleContent(url.pathname);
renderArticlePage(articleContent);
},
});
}
});
Using focusReset and scroll
Form submission can be detected by querying for the NavigateEvent.formData property. The following example turns any form submission into one which stays on the current page. In this case, you don't update the DOM, so you can cancel any default reset and scroll behavior using focusReset and scroll.
navigation.addEventListener("navigate", (event) => {
if (event.formData && event.canIntercept) {
// User submitted a POST form to a same-domain URL
// (If canIntercept is false, the event is just informative:
// you can't intercept this request, although you could
// likely still call .preventDefault() to stop it completely).
event.intercept({
// Since we don't update the DOM in this navigation,
// don't allow focus or scrolling to reset:
focusReset: "manual",
scroll: "manual",
async handler() {
await fetch(event.destination.url, {
method: "POST",
body: event.formData,
});
// You could navigate again with {history: 'replace'} to
// change the URL here, which might indicate "done"
},
});
}
});
Specifications
| Specification |
|---|
| HTML> # dom-navigateevent-intercept-dev> |
Browser compatibility
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