Articles Tagged JavaScript

​​​​Uncaught TypeError: Cannot read property 'foo' of undefined.​ The dreaded error we all hit at some point in JavaScript development. Could be an empty state from an API that returns differently than you expected. Could be something else. We don’t know because the error itself is so general and broad.

​​I recently had an issue where certain environment variables weren't being pulled in for one reason or another, causing all sorts of funkiness with that error staring me … Read article

Around this time last year, I wrote an article about the JavaScript learning landscape. Within that article, you’ll find my grand plans to learn JavaScript — complete with a link to a CodePen Collection I started for tracking my progress, and it even got dozens of comments cheering me on.

Like most people, I was ambitious. It was a new year and I was excited to tackle a long-standing project. It was my development version of losing 30 pounds … Read article

A common need when writing vanilla JavaScript is to find a selection of elements in the DOM and loop over them. For example, finding instances of a button and attaching a click handler to them.

const buttons = document.querySelectorAll(".js-do-thing");
// There could be any number of these! 
// I need to loop over them and attach a click handler.

There are SO MANY ways to go about it. Let's go through them.… Read article

Many people have messaged me, confused about where to get started with testing. Just like everything else in software, we work hard to build abstractions to make our jobs easier. But that amount of abstraction evolves over time, until the only ones who really understand it are the ones who built the abstraction in the first place. Everyone else is left with taking the terms, APIs, and tools at face value and struggling to make things work.

One thing I … Read article

Writing asynchronous JavaScript without using the Promise object is a lot like baking a cake with your eyes closed. It can be done, but it's gonna be messy and you'll probably end up burning yourself.

I won't say it's necessary, but you get the idea. It's real nice. Sometimes, though, it needs a little help to solve some unique challenges, like when you're trying to sequentially resolve a bunch of promises in order, one after the other. A trick … Read article

Let's say you wanted to move the background-position on an element as you mouse over it to give the design a little pizzazz. You have an element like this:

<div class="module" id="module"></div>

And you toss a background on it:

.module {
  background-image: url(big-image.jpg);
}

You can adjust the background-position in JavaScript like this:

const el = document.querySelector("#module");

el.addEventListener("mousemove", (e) => {
  el.style.backgroundPositionX = -e.offsetX + "px";
  el.style.backgroundPositionY = -e.offsetY + "px";
});

This is a possible upcoming feature for mobile Chrome:

If a Data Saver user is on a 2G-speed or slower network according to the NetInfo API, Chrome disables scripts and sends an intervention header on every resource request. Users are shown a UI at the bottom of the screen indicating the page has been modified to save data. Users can enable scripts on the page by tapping “Show original” in the UI.