While redesigning my photography website, I've looked into the Open Graph (OG) images, which are displayed when sharing a link on social media or messaging apps. Here's an example from WhatsApp: For each photo that I publish, I create a WebP thumbnail for the gallery. I wanted to use those as OG images, but the WebP support was lacking, so I've been creating an additional JPG variant just for Open Graph. I was interested in seeing how things have changed in the last 2.5 years. I've tested the following platforms: WhatsApp, Telegram, Signal, Discord, Slack, Teams, Facebook, LinkedIn, Xing, Bluesky, Threads and Phanpy (Mastodon). Here are the results: All providers support JPEG and PNG. All providers except Teams and Xing support WebP. No provider except Facebook supports AVIF. WhatsApp displays the AVIF image, but the colors are broken. "X, formerly Twitter" didn't display OG images for my test pages at all. I don't care about that platform, so I didn't bother to further investigate. Those results confirmed that I could now use WebP Open Graph images without creating an additional JPG file.

I'm a frequent user of bookmarklets. As I'm sharing some of them on my blog, I wrote this post to explain what bookmarklets are and how to use them. In short, a bookmarklet is a browser bookmark containing JavaScript code. Clicking the bookmark executes the script in the context of the current web page, allowing users to perform tasks such as modifying the appearance of a webpage or extracting information. Bookmarklets are a simpler, more lightweight alternative to browser extensions, Chrome snippets, and userscripts. How to add a bookmarklet? Here's an example to display a browser dialog with the title of the current web page: Display page title You can click the link to see what it does. To run this script on other websites, we have to save it as a bookmarklet. My preferred way is to drag the link onto the bookmarks toolbar: A link on a web page is dragged and dropped onto a browser bookmark bar. A bookmark creation dialog appears. The prompt is confirmed and closed. The created bookmarklet is clicked. The current web page title is displayed in a browser dialog. Another way is to right-click the link to open its context menu: In Firefox, you can then select "Bookmark Link…". Other browsers make it a little more difficult: select "Copy Link (Address)", manually create a new bookmark, and then paste the copied URL as the link target. Once created, you can click the bookmark(let) on any web page to display its title. Scroll further down to see more useful use cases. How to write a bookmarklet? Let's start with the code for the previous bookmarklet example: window.alert(document.title) To turn that script into a bookmarklet, we have to put javascript: in front of it: javascript:window.alert(document.title) To keep our code self-contained, we should wrap it with an IIFE (immediately invoked function expression): javascript:(() => { window.alert(document.title) })() Finally, you might have to URL-encode your bookmarklet if you get issues with special characters: javascript:%28%28%29%20%3D%3E%20%7B%0A%20%20window.alert%28document.title%29%0A%7D%29%28%29 Useful bookmarklets Here are some bookmarklets I've created: Debugger — Starts the browser DevTools debugger after 3 seconds, useful for debugging dynamic content changes. Log Focus Changes — Logs DOM elements when the focus changes. Design Mode — Makes the web page content-editable (toggle).

It can be frustrating to fill out a web form, only to accidentally refresh the page (or click "back") and lose all the hard work. In this blog post, I present a method to retain form data when the page is reloaded, which improves the user experience. Browser behavior Most browsers provide an autofill feature. In the example form below, enter anything into the input field. Then, try out the following: Click the "Example link" and use the "back" functionality of your browser. Reload the page. Query Example link Depending on your browser, the input value might be restored: Browser Reload Back Firefox 130 Yes Yes Chrome 129 No Yes Safari 18 No Yes How does it work? I was surprised to learn that this autofill behavior is controlled via the autocomplete, that is mostly used for value autocompletion from past web forms. However, if we disable the autocompletion, the autofill feature will be disabled as well: <input autocomplete="false" /> To learn more about the behavior, read the full spec on persisted history entry state. Preserving application state Even with autofill, no browser will restore dynamic changes previously triggered by the user. In the following example, the user has to always press the "Search" button to view the results: This is an interactive example. Please enable JavaScript to use it. Query Search ... const inputElementNative = document.querySelector("#example-search-input"); const outputElementNative = document.querySelector("#example-search-output"); const performSearch_exampleSearch = (outputElement) => { outputElement.innerText = ""; const introText = document.createTextNode("Open the result for "); outputElement.appendChild(introText); const link = document.createElement("a"); link.href = "https://example.com"; link.innerText = inputElementNative.value || "no text"; outputElement.appendChild(link); }; document.querySelector("#example-search-form").addEventListener("submit", (event) => { event.preventDefault(); performSearch_exampleSearch(outputElementNative); }, ); If the web page changes its content after user interaction, it might be a good idea to restore the UI state after the page has been refreshed. For example, it's useful to restore previous search results for an on-site search. Note that Chrome will fire a change event on inputs, but this is considered a bug as the respective spec has been updated. Storing form values As the form value might be lost on reload, we need to store it temporarily. Some common places to store data include local storage, session storage, cookies, query parameters or hash. They all come with drawbacks for our use case, though. Instead, I suggest using the browser history state, which has several advantages: We get data separation between multiple browser tabs with no additional effort. The data is automatically cleaned up when the browser tab is closed. We don't pollute the URL and prevent page reloads. Let's store the search input value as query: document.querySelector("form").addEventListener("submit", (event) => { event.preventDefault(); const inputElement = document.querySelector("input"); history.replaceState({ query: inputElement.value }, ""); performSearch(); }); This example uses the submit event to store the data, which fits our "search" use case. In a regular form, using the input change event might be a better trigger to store form values. Using replaceState over pushState will ensure that no unnecessary history entry is created. Uncaught TypeError: Failed to execute 'replaceState' on 'History': 2 arguments required, but only 1 present. Restoring form values My first approach to restore form values was to listen to the pageshow event. Once it's fired, we can access the page load type from window.performance: window.addEventListener("pageshow", () => { const type = window.performance.getEntriesByType("navigation")[0].type; const query = history.state?.query; if (query && (type === "back_forward" || type === "reload")) { document.querySelector("#my-input").value = query; performSearch(); } }); I will keep the solution here in case someone needs it, but usually it is unnecessary to check the page load type. Because the history state is only set after the search form has been submitted, we can check the state directly: const query = history.state?.query; if (query) { document.querySelector("#my-input").value = query; performSearch(); } Demo Here's an example combining both techniques to store and restore the input value: This is an interactive example. Please enable JavaScript to use it. Query Search ... const inputElementCustom = document.querySelector("#example-preserve-input"); const outputElementCustom = document.querySelector("#example-preserve-output"); const performSearch_examplePreserve = (outputElement) => { outputElement.innerText = ""; const introText = document.createTextNode("Open the result for "); outputElement.appendChild(introText); const link = document.createElement("a"); link.href = "https://example.com"; link.innerText = inputElementCustom.value || "no text"; outputElement.appendChild(link); }; document.querySelector("#example-preserve-form").addEventListener("submit", (event) => { event.preventDefault(); performSearch_examplePreserve(outputElementCustom); history.replaceState({ query: inputElementCustom.value }, ""); }); const historyQuery = history.state?.query; if (historyQuery) { document.querySelector("#example-preserve-input").value = historyQuery; performSearch_examplePreserve(outputElementCustom); } Conclusion Preserving form data on page refresh is a small but impactful way to improve user satisfaction. The default browser autofill feature handles only basic use cases, so ideally we should maintain the form state ourselves. In this blog post, I've explained how to use the browser history state to temporarily store and retrieve form values.

In this post, I will summarize some problems and constraints that I've encountered with the Notifications and Push web APIs. Notification settings on macOS Someone who's definitely not me wasted half an hour wondering why triggered notifications would not appear. On macOS, make sure to enable system notifications for your browsers. Open "System Settings" → "Notifications". For each browser, select "Allow notifications" and set the appearance to "Alerts": Onchange listener not called Web APIs offer a way to subscribe to change events. This is especially useful in React: navigator.permissions .query({ name: "push", userVisibleOnly: true }) .then((status) => { status.onchange = function () { // synchronize permission status with local state setNotificationPermission(this.state); }; }); Whenever the notification permission changes (either through our application logic or via browser controls), we can synchronize the UI in real-time according to the current permission value (prompt, denied or granted). However, due to a Firefox bug, the event listener callback is never called. This means that we can't react to permission changes via browser controls in Firefox. That's especially unfortunate when combined with push messages, where we want to subscribe the user once they grant the notification permission. One workaround is to check at page load if the notification permission is granted with no valid subscription and resubscribe the user. Notification image not supported Browser notifications support an optional image property. This property is marked as "experimental", so it's not surprising that some browsers (Firefox, Safari) don't support it. There is an open feature request to add support in Firefox, but it has been open since 2019. VAPID contact information required When sending a push message, we have to provide VAPID parameters (e.g. the public and private key). According to the specification, the sub property (contact email or link) is optional: If the application server wishes to provide, the JWT MAY include a "sub" (Subject) claim. Despite this specification, the Mozilla push message server will return an error if the subject is missing: 401 Unauthorized for (...) and subscription https://updates.push.services.mozilla.com/wpush/v2/… You might not encounter this issue when using the popular web-push npm package, as its API encourages you to provide the subject as the first parameter: webpush.setVapidDetails("hello@example.com", publicKey, privateKey); However, in the webpush-java library, you need to set the subject explicitly: builder.subject("hello@example.com"); There is an open issue with more information about this problem. Microsoft Edge pitfalls Microsoft introduced adaptive notification requests in the Edge browser. It is a crowdsourced score system, which may auto-accept or auto-reject notification requests. The behavior can be changed in the Edge notification settings. Additionally, on a business or school device, those settings might be fixed, displaying the following tooltip: This setting is managed by your organization.