How to Create a Diff of Two Images

When I was a child, I loved looking for Waldo in the “Where’s Waldo?” book series. These days I’m a sucker for TMZ’s “What’s the Big Frigin Difference” images, where TMZ slightly changes an image and you have to spot the differences between the two. That got me to thinking — how easily could I […]

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fetch with Timeout

A few years back I wrote a blog post about how write a fetch Promise that times out. The function was effective but the code wasn’t great, mostly because AbortController , which allows you to cancel a fetch Promise, did not yet exist. With AbortController and AbortSignal available, let’s create a better JavaScript function for […]

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Customizing HTML Form Validation

Form validation has always been my least favorite part of web development. You need to duplicate validation on both client and server sides, handle loads of events, and worry about form element styling. To aid form validation, the HTML spec added some new form attributes like required and pattern to act as very basic validation. […]

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How to Determine a JavaScript Promise’s Status

Promises have changed the landscape of JavaScript. Many old APIs have been reincarnated to use Promises (XHR to fetch, Battery API), while new APIs trend toward Promises. Developers can use async/await to handle promises, or then/catch/finally with callbacks, but what Promises don’t tell you is their status. Wouldn’t it be great if the Promise.prototype provided […]

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Detect XR Support with JavaScript

A few years ago I wrote an article about how to detect VR support with JavaScript. Since that time, a whole lot has changed. “Augmented reality” became a thing and terminology has moved to “XR”, instead of VR or AR. As such, the API has needed to evolve. The presence of navigator.xr signals that the […]

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Document.elementFromPoint

Reacting to events with JavaScript is the foundation of a dynamic experiences on the web. Whether it’s a click event or another typical action, responding to that action is important. We started with assigning events to specific elements, then moved to event delegation for efficiency, but did you know you can identify elements by position […]

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Detect Browser Bars Visibility with JavaScript

It’s one thing to know about what’s in the browser document, it’s another to have insight as to the user’s browser itself. We’ve gotten past detecting which browser the user is using, and we’re now into knowing what pieces of the browser UI users are seeing. Browsers provide window.personalbar, window.locationbar, and window.menubar properties, with the […]

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JavaScript print Events

Media queries provide a great way to programmatically change behavior depending on viewing state. We can target styles to device, pixel ratio, screen size, and even print. That said, it’s also nice to have JavaScript events that also allow us to change behavior. Did you know you’re provided events both before and after printing? I’ve […]

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How to Control CSS Animations with JavaScript

When it comes to animations on the web, developers need to measure the animation’s requirements with the right technology — CSS or JavaScript. Many animations are manageable with CSS but JavaScript will always provide more control. With document.getAnimations, however, you can use JavaScript to manage CSS animations! The document.getAnimations method returns an array of CSSAnimation […]

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