ResizeObserver is a JavaScript web API that allows you to run code whenever an element’s size changes.

Before getting into the ResizeObserver, let’s first get refreshed on the different boxes HTML elements are made of. A standard element, take a <div> for example, consists of a content box, and border box. The content box, depicted in blue in the image below, consists of all the content within the padding of the element. The border box consists of the border and everything within it.

As a web developer, you may want to choose which box size is relevant for your application, and use ResizeObserver to track changes to the dimensions of that box. If it’s just the content-box…


Many Sky-Watcher telescopes come with a decent quality 8x50 finder scope. I converted my scope into a guide scope for use with a ZWO ASI 120mm Mini.

The telescope I use for backyard astronomy and astrophotography is a Sky-Watcher EvoStar 100ED. It came with an 8x50 right angle finder scope (8x magnification with an aperture of 50mm). Since this is roughly the size of the average guidescope, I thought I could convert this to one. There are many people who have done this and there are plenty of posts about it in forums such as CloudyNights. Most people use this adapter to connect their camera to the scope. I thought I could save money and have it 3D printed instead.

I’m not much of an expert in…

Sahir Vellani

Software Engineer @ Microsoft | Web Platform | Amateur Astrophotographer

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