Extract a Number from a String with JavaScript

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User input from HTML form fields is generally provided to JavaScript as a string. We’ve lived with that fact for decades but sometimes developers need to extract numbers from that string. There are multiple ways to get those numbers but let’s rely on regular expressions to extract those numbers! To employ a regular expression to get a number within a string, we can use \d+: const string = "x12345david"; const [match] = string.match(/(\d+)/); match; // 12345 Regular expressions are capable of really powerful operations within JavaScript; this practice is one of the easier operations. Converting the number using a Number() wrapper will give you the number as a Number type. The... more →
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Sum an Array of Numbers with JavaScript

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It’s rare that I’m disappointed by the JavaScript language not having a function that I need. One such case was summing an array of numbers — I was expecting Math.sum or a likewise, baked in API. Fear not — summing an array of numbers is easy using Array.prototype.reduce! const numbers = [1, 2, 3, 4]; const sum = numbers.reduce((a, b) =a + b, 0); The 0 represents the starting value while with a and b, one represents the running total with the other representing the value to be added. You’ll also note that using reduce prevents side effects! I’d still prefer something like Math.sum(...numbers) but a simple reduce will do! The post Sum an Array of Numbers... more →
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JavaScript waitFor Polling

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As more of the JavaScript developers write becomes asynchronous, it’s only natural to need to wait for conditions to be met. This is especially true in a world with asynchronous testing of conditions which don’t provide an explicit await. I’ve written about waitForever, waitForTime, and JavaScript Polling in the past, but I wanted to have a more modern way of awaiting a given state. Let’s have a look at this super useful waitFor function! waitFor is an async function that allows developers to provide a condition function, polling interval (in milliseconds), and optional timeout (in milliseconds). // Polls every 50 milliseconds for a given condition const waitFor = async... more →
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JavaScript closest

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When it comes to finding relationships between elements, we traditionally think of a top-down approach. We can thank CSS and querySelector/querySelectorAll for that relationship in selectors. What if we want to find an element’s parent based on selector? To look up the element tree and find a parent by selector, you can use HTMLElement‘s closest method: // Our sample element is an "a" tag that matches ul > li > a const link = document.querySelector('li a'); const list = a.closest('ul'); closest looks up the ancestor chain to find a matching parent element — the opposite of traditional CSS selectors. You can provide closest a simple or complex selector to look upward... more →
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JavaScript: Reverse Arrays

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Manipulating data is core to any programming language. JavaScript is no exception, especially as JSON has token over as a prime data delivery format. One such data manipulation is reversing arrays. You may want to reverse an array to show most recent transactions, or simple alphabetic sorting. Reversing arrays with JavaScript originally was done via reverse but that would mutate the original array: // First value: const arr = ['hi', 'low', 'ahhh']; // Reverse it without reassigning: arr.reverse(); // Value: arr (3) ['ahhh', 'low', 'hi'] Modifying the original array is a legacy methodology. To avoid this mutation, we’d copy the array and then reverse it: const reversed = [...arr].reverse();... more →
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Updating and Supporting URL Parameters in JavaScript

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Not quite a long time ago, but roughly two years ago I wrote a blog post on updating and supporting, URL parameters with Vue.js. The idea was this: Given an application that lets you perform various tweaks, it would be nice if the URL was updated to reflect the current state of the application. This would let you bookmark, or share, the URL with others and they would get the same view as you. In that post, I built a very basic "data filtering" application and then updated it to support updates to the URL. I thought I’d revisit that post and demonstrate building it in vanilla JavaScript. As always, I’d love to hear your thoughts on this, especially if you’ve done something... more →
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JavaScript Array Group

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Managing, sorting, and manipulating data with JavaScript is a skill we’ve often delegated to third party libraries like lodash. As the JavaScript language progresses, however, these features eventually get. added to the JavaScript specification. Two such APIs for grouping of Array data are `Array.prototype.group and Array.prototype.groupToMap. Array.prototype.group To group an array of objects by a given property, call the group method with function that returns the grouping string: const teams = [ { name: "Arsenal", origin: "London", tier: "legendary" }, { name: "Manchester United", origin: "Manchester", tier: "legendary" }, { name: "Liverpool", origin: "Liverpool", tier: "legendary"... more →
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How to Control CSS Animations with JavaScript

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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 objects. CSSAnimation provides a host of information about the animation: playState, timeline, effect, and events like onfinish. You can then modify those objects to adjust animations: // Make all CSS animations on the page twice as fast document.getAnimations().forEach((animation) ={ animation.playbackRate... more →
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