Siema – Lightweight and simple carousel with no dependencies

Siema is a lightweight (only 3kb gzipped) carousel plugin with no dependencies and no styling.It is 100% open source and available on Github. It is free to use on personal and commercial projects. Use it with your favourite module bundler or by manually injecting the script into your project.

I especially like the fact that it’s standalone and can easily be implemented into any existing code. The options you can pass into it (shown below), and API it exposes are exactly those I’d expect from such a library.

new Siema({
  selector: '.siema',
  duration: 200,
  easing: 'ease-out',
  perPage: 1,
  startIndex: 0,
  draggable: true,
  multipleDrag: true,
  threshold: 20,
  loop: false,
  rtl: false,
  onInit: () => {},
  onChange: () => {},

Installation per yarn/npm

yarn add siema

Siema – Lightweight and simple carousel with no dependencies →

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Sticky Events – Events for position: sticky;

Sticky Events is a library that can listen for events on elements that have position: sticky; applied. It’s an abstraction built on top of the IntersectionObserver, and provides one with three types of events:

  • StickyEvent.CHANGE: Fired when an element becomes stuck or unstuck
  • StickyEvent.STUCK: Fired only when an element becomes stuck
  • StickyEvent.UNSTUCK: Fired only when an element becomes unstuck

Usage is quite simple: set up it once, and then add event listeners to the elements:

import { observeStickyEvents, StickyEvent } from "sticky-events";

// Add listeners to all `.sticky-events` elements on the page

// Events are dispatched on elements with the `.sticky-events` class
const stickies = Array.from(document.querySelectorAll('.sticky-events'));

stickies.forEach((sticky) => {
  sticky.addEventListener(StickyEvent.CHANGE, (event) => {
    sticky.classList.toggle('bg-dark', event.detail.isSticky);

  sticky.addEventListener(StickyEvent.STUCK, (event) => {

  sticky.addEventListener(StickyEvent.UNSTUCK, (event) => {

Sticky Events – Events for position: sticky;

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Responsive UIs in React Native

On the web it is – by now – obvious that you make your website responsive (*). Using a listener listening to the change event of the Dimensions API, it’s also possible to implement this kind of behaviour in React Native.

import {Component} from "react";
import {Dimensions} from "react-native";

export default class LogDimensionChanges extends Component {
    state = Dimensions.get("window");
    handler = dims => this.setState(dims);

    componentWillMount() {
        Dimensions.addEventListener("change", this.handler);

    componentWillUnmount() {
      // Important to stop updating state after unmount
      Dimensions.removeEventListener("change", this.handler);

    render() {
        const {width, height} = this.state.window;
        const mode = height > width ? "portrait" : "landscape";
        console.log(`New dimensions ${width}x${height} (${mode})`);
        return null;

This logic is applied into the react-native-responsive-ui package, which provides you with a <MediaQuery /> component, ResponsiveStyleSheet class, etc.:

import React, {Component} from "react";
import {View} from "react-native";
import {MediaQuery} from "react-native-responsive-ui";

export default class Login extends Component {
    render(): React$Element<*> {
        return <View>
            <MediaQuery minHeight={450} orientation="portrait">
                <Logo />

Responsive UIs in React Native →

(*) I know, this site still uses a non-responsive WordPress theme … shame on me

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Dynamic Bézier Curves

Nice writeup by Josh Comeau on how he created the on-scroll-animated bézier curve on his website

Did you notice that as you started scrolling on this page, the Bézier curves that border the green title hero thingy started flattening? Keep your eye on the swoopy curves just above the post text as you scroll through the top of the document. Notice how they become flat as they approach the header at the top of the viewport?

In a delightful bit of serendipity, I realized while building the blog that this feature would make a great first blog post!

Love the interactive examples embedded into the post. They really help convey the message.

Dynamic Bézier Curves →

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How to display a “new version available” for a Progressive Web App

Dean Hume:

I’ve built a number of Progressive Web Apps that simply update the service worker silently for the user in the background, but I really like the approach where you get a popup notification that suggests that there is a new version of the site available like Google’s Inbox provides – especially for an offline first web app. […] It got me wondering how I could build something a little similar and it turns out that it is a little tricker than it seems – but it is not impossible!

How to display a “new version available” for a Progressive Web App →

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10x Performance Increases: Optimizing a Static Site

Use case by JonLuca De Caro in which he optimised the page load speed of a static site. Before optimisation the site weighed 1MB (at 20 requests) with DOMContentLoaded at 3.74s. After optimisation the site weighed only 267kB (at 9 requests) with DOMContentLoaded at 197ms.

10x Performance Increases: Optimizing a Static Site →

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JavaScript asyncawait: Resolving Promises in parallel

Recently I saw a colleague implement some functionality in which he required two results from an API using asyncawait. The piece of code looked something like this:

The code looks fine, is syntactically correct, and works … but there’s one big problem with it: the calls are made sequentially.

To run these calls – which are promises – in parallel, one can reside to using Promise.all. Combine that with destructuring and the code becomes this:

Easy, right?

💻 The example embedded in this post is part of a talk on ESNext named “What’s next
 for JavaScript?”, which I recently gave at a Fronteers België meetup and Frontend United 2018 (Utrecht). You can check out the slides / a recording of that talk right here. I’m available for bringing this talk at your meetup/conference.

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Resilient, Declarative, Contextual

I enjoyed reading this piece by Keith J. Grant on three key characteristics of CSS that set it apart from conventional programming languages.

I want to look at three key characteristics of CSS that set it apart from conventional programming languages: it’s resilient; it’s declarative; and it’s contextual. Understanding these aspects of the language, I think, is key to becoming proficient in CSS.

Resilient, Declarative, Contextual →

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A JavaScript Typing Carousel

I like this JS typewriter effect:

The HTML that goes along with that is really simple:

<h1>This pen is
     data-rotate='[ "nerdy.", "simple.", "pure JS.", "pretty.", "fun!" ]'></span>

Simple Typing Carousel →

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Harry Roberts: FaCSSt – CSS and Performance

A Frontend United I was lucky to see Harry Roberts give this talk on CSS and Performance. You can watch it to, as the recording has been published to YouTube

Ahh… CSS and performance. Two of my favourite things! But how well do they play together? It depends…

In this very matter-of-fact talk, we’ll be looking at all of the different ways CSS can make our websites faster or slower. From the common and perhaps more obvious, to the unusual and obscure ways in which CSS can impact performance for better or worse.

Great content. And great to see that I’m not the only one mentioning the answer to life, the universe, web development and usability from time to time.

Sidenote: A recording of my talk “What’s next for JavaScript” at Fronted United is also available. Always confronting to see yourself speak … learnt a lot from watching that.

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