How to Create and Publish Web Components with Vue.js

How to Create and Publish Web Components with Vue.js

In this article, we will build a weather widget web component that displays the weather from the OpenWeatherMap API. We will add a search to let users look up the current weather and forecast from the API.

Component-based architecture is the main architecture for front end development today. The World Wide Web Consortium (W3C) has caught up to the present by creating the web components API. It lets developers build custom elements that can be embedded in web pages. The elements can be reused and nested anywhere, allowing for code reuse in any pages or apps.

The custom elements are nested in the shadow DOM, which is rendered separately from the main DOM of a document. This means that they are completely isolated from other parts of the page or app, eliminating the chance of conflict with other parts,

There are also template and slot elements that aren’t rendered on the page, allowing you to reused the things inside in any place.

To create web components without using any framework, you have to register your element by calling CustomElementRegistry.define() and pass in the name of the element you want to define. Then you have to attach the shadow DOM of your custom element by calling Element.attachShawdow() so that your element will be displayed on your page.

This doesn’t include writing the code that you want for your custom elements, which will involve manipulating the shadow DOM of your element. It is going to be frustrating and error-prone if you want to build a complex element.

Vue.js abstracts away the tough parts by letting you build your code into a web component. You write code by importing and including the components in your Vue components instead of globally, and then you can run commands to build your code into one or more web components and test it.

We build the code into a web component with Vue CLI by running:

npm run build -- --target wc --inline-vue --name custom-element-name

The --inline-vue flag includes a copy of view in the built code, --target wc builds the code into a web component, and --name is the name of your element.

In this article, we will build a weather widget web component that displays the weather from the OpenWeatherMap API. We will add a search to let users look up the current weather and forecast from the API.

We will use Vue.js to build the web component. To begin building it, we start with creating the project with Vue CLI. Run npx @vue/cli create weather-widget to create the project. In the wizard, select Babel, SCSS and Vuex.

The OpenWeatherMap API is available at https://openweathermap.org/api. You can register for an API key here. Once you got an API key, create an .env file in the root folder and add VUE_APP_APIKEY as the key and the API key as the value.

Next, we install some packages that we need for building the web component. We need Axios for making HTTP requests, BootstrapVue for styling, and Vee-Validate for form validation. To install them, we run npm i axios bootstrap-vue vee-validate to install them.

With all the packages installed we can start writing our code. Create CurrentWeather.vue in the components folder and add:

<template>
  <div>
    <br />
    <b-list-group v-if="weather.main">
      <b-list-group-item>Current Temparature: {{weather.main.temp - 273.15}} C</b-list-group-item>
      <b-list-group-item>High: {{weather.main.temp_max - 273.15}} C</b-list-group-item>
      <b-list-group-item>Low: {{weather.main.temp_min - 273.15}} C</b-list-group-item>
      <b-list-group-item>Pressure: {{weather.main.pressure }}mb</b-list-group-item>
      <b-list-group-item>Humidity: {{weather.main.humidity }}%</b-list-group-item>
    </b-list-group>
  </div>
</template>

<script>
import { requestsMixin } from "@/mixins/requestsMixin";
import store from "../store";
import { BListGroup, BListGroupItem } from "bootstrap-vue";
import 'bootstrap/dist/css/bootstrap.css'
import 'bootstrap-vue/dist/bootstrap-vue.css'

export default {
  store,
  name: "CurrentWeather",
  mounted() {},
  mixins: [requestsMixin],
  components: {
    BListGroup,
    BListGroupItem
  },
  computed: {
    keyword() {
      return this.$store.state.keyword;
    }
  },
  data() {
    return {
      weather: {}
    };
  },
  watch: {
    async keyword(val) {
      const response = await this.searchWeather(val);
      this.weather = response.data;
    }
  }
};
</script>

<style scoped>
p {
  font-size: 20px;
}
</style>

This component displays the current weather from the OpenWeatherMap API as the keyword from the Vuex store is updated. We will create the Vuex store later. The this.searchWeather function is from the requestsMixin , which is a Vue mixin that we will create. The computed block gets the keyword from the store via this.$store.state.keyword and return the latest value.

Note that we’re importing all the BootstrapVue components individually here. This is because we aren’t building an app. main.js in our project will not be run, so we cannot register components globally by calling Vue.use . Also, we have to import the store here, so that we have access to the Vuex store in the component.

Next, create Forecast.vue in the same folder and add:

<template>
  <div>
    <br />
    <b-list-group v-for="(l, i) of forecast.list" :key="i">
      <b-list-group-item>
        <b>Date: {{l.dt_txt}}</b>
      </b-list-group-item>
      <b-list-group-item>Temperature: {{l.main.temp - 273.15}} C</b-list-group-item>
      <b-list-group-item>High: {{l.main.temp_max - 273.15}} C</b-list-group-item>
      <b-list-group-item>Low: {{l.main.temp_min }}mb</b-list-group-item>
      <b-list-group-item>Pressure: {{l.main.pressure }}mb</b-list-group-item>
    </b-list-group>
  </div>
</template>

<script>
import { requestsMixin } from "@/mixins/requestsMixin";
import store from "../store";
import { BListGroup, BListGroupItem } from "bootstrap-vue";
import 'bootstrap/dist/css/bootstrap.css'
import 'bootstrap-vue/dist/bootstrap-vue.css'

export default {
  store,
  name: "Forecast",
  mixins: [requestsMixin],
  components: {
    BListGroup,
    BListGroupItem
  },
  computed: {
    keyword() {
      return this.$store.state.keyword;
    }
  },
  data() {
    return {
      forecast: []
    };
  },
  watch: {
    async keyword(val) {
      const response = await this.searchForecast(val);
      this.forecast = response.data;
    }
  }
};
</script>

<style scoped>
p {
  font-size: 20px;
}
</style>

It’s very similar to CurrentWeather.vue . The only difference is that we are getting the current weather instead of the weather forecast.

Next, we create a mixins folder in the src folder and add:

const APIURL = "http://api.openweathermap.org";
const axios = require("axios");

export const requestsMixin = {
  methods: {
    searchWeather(loc) {
      return axios.get(
        `${APIURL}/data/2.5/weather?q=${loc}&appid=${process.env.VUE_APP_APIKEY}`
      );
    },
		
searchForecast(loc) {
      return axios.get(
        `${APIURL}/data/2.5/forecast?q=${loc}&appid=${process.env.VUE_APP_APIKEY}`
      );
    }
  }
};

These functions are for getting the current weather and the forecast respectively from the OpenWeatherMap API. process.env.VUE_APP_APIKEY is obtained from our .env file that we created earlier.

Next in App.vue , we replace the existing code with:

<template>
  <div>
    <b-navbar toggleable="lg" type="dark" variant="info">
      <b-navbar-brand href="#">Weather App</b-navbar-brand>
    </b-navbar>
    <div class="page">
      <ValidationObserver ref="observer" v-slot="{ invalid }">
        <b-form @submit.prevent="onSubmit" novalidate>
          <b-form-group label="Keyword" label-for="keyword">
            <ValidationProvider name="keyword" rules="required" v-slot="{ errors }">
              <b-form-input
                :state="errors.length == 0"
                v-model="form.keyword"
                type="text"
                required
                placeholder="Keyword"
                name="keyword"
              ></b-form-input>
              <b-form-invalid-feedback :state="errors.length == 0">Keyword is required</b-form-invalid-feedback>
            </ValidationProvider>
          </b-form-group>
					
<b-button type="submit" variant="primary">Search</b-button>
        </b-form>
      </ValidationObserver>
			
<br />

<b-tabs>
        <b-tab title="Current Weather">
          <CurrentWeather />
        </b-tab>
        <b-tab title="Forecast">
          <Forecast />
        </b-tab>
      </b-tabs>
    </div>
  </div>
</template>

<script>
import CurrentWeather from "@/components/CurrentWeather.vue";
import Forecast from "@/components/Forecast.vue";
import store from "./store";
import {
  BTabs,
  BTab,
  BButton,
  BForm,
  BFormGroup,
  BFormInvalidFeedback,
  BNavbar,
  BNavbarBrand,
  BFormInput
} from "bootstrap-vue";
import { ValidationProvider, extend, ValidationObserver } from "vee-validate";
import { required } from "vee-validate/dist/rules";
extend("required", required);

export default {
  store,
  name: "App",
  components: {
    CurrentWeather,
    Forecast,
    ValidationProvider,
    ValidationObserver,
    BTabs,
    BTab,
    BButton,
    BForm,
    BFormGroup,
    BFormInvalidFeedback,
    BNavbar,
    BNavbarBrand,
    BFormInput
  },
  data() {
    return {
      form: {}
    };
  },
  methods: {
    async onSubmit() {
      const isValid = await this.$refs.observer.validate();
      if (!isValid) {
        return;
      }
      localStorage.setItem("keyword", this.form.keyword);
      this.$store.commit("setKeyword", this.form.keyword);
    }
  },
  beforeMount() {
    this.form = { keyword: localStorage.getItem("keyword") || "" };
  },
  mounted() {
    this.$store.commit("setKeyword", this.form.keyword);
  }
};
</script>

<style lang="scss">
@import "./../node_modules/bootstrap/dist/css/bootstrap.css";
@import "./../node_modules/bootstrap-vue/dist/bootstrap-vue.css";
.page {
  padding: 20px;
}
</style>

We add the BootstrapVue b-navbar here to add a top bar to show the extension’s name. Below that, we added the form for searching the weather info. Form validation is done by wrapping the form in the ValidationObserver component and wrapping the input in the ValidationProvider component. We provide the rule for validation in the rules prop of ValidationProvider . The rules will be added in main.js later.

The error messages are displayed in the b-form-invalid-feedback component. We get the errors from the scoped slot in ValidationProvider . It’s where we get the errors object from.

When the user submits the number, the onSubmit function is called. This is where the ValidationObserver becomes useful as it provides us with the this.$refs.observer.validate() function to check for form validity.

If isValid resolves to true , then we set the keyword in local storage, and also in the Vuex store by running this.$store.commit(“setKeyword”, this.form.keyword); .

In the beforeMount hook, we set the keyword so that it will be populated when the extension first loads if a keyword was set in local storage. In the mounted hook, we set the keyword in the Vuex store so that the tabs will get the keyword to trigger the search for the weather data.

Like in the previous components, we import and register all the components and the Vuex store in this component, so that we can use the BootstrapVue components here. We also called Vee-Validate’s extend function so that we can use its required form validation rule for checking the input.

In style section of this file, we import the BootstrapVue styles, so that they can be accessed in this and the child components. We also add the page class so that we can add some padding to the page.

Then in store.js , we replace the existing code with:

import Vue from "vue";
import Vuex from "vuex";

Vue.use(Vuex);

export default new Vuex.Store({
  state: {
    keyword: ""
  },
  mutations: {
    setKeyword(state, payload) {
      state.keyword = payload;
    }
  },
  actions: {}
});

to add the Vuex store that we referenced in the components. We have the keyword state for storing the search keyword in the store, and the setKeyword mutation function so that we can set the keyword in our components.

Finally, in package.json , we add 2 scripts to the scripts section of the file:

"wc-build": "npm run build -- --target wc --inline-vue --name weather-widget",

"wc-test": "cd dist && live-server --port=8080 --entry-file=./demo.html"

The wc-build script builds our code into a web component as we described before, and the wc-test runs a local web server so that we can see what the web component looks like when it’s included in a web page. We use the live-server NPM package for serving the file. The --entry-file option specifies that we server demo.html as the home page, which we get when we run npm run wc-build .

If we run npm run wc-build and npm run wc-test , we get:

As you can see, we get the web component’s shadow DOM rendered in the browser and in the developer console.

We created a web component with less effort than using plain JavaScript, especially for something complex enough to have nesting and interactions.

Thank you for reading !

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JavaScript developers should you be using Web Workers?

JavaScript developers should you be using Web Workers?

Do you think JavaScript developers should be making more use of Web Workers to shift execution off of the main thread?

Originally published by David Gilbertson at https://medium.com

So, Web Workers. Those wonderful little critters that allow us to execute JavaScript off the main thread.

Also known as “no, you’re thinking of Service Workers”.

Photo by Caleb Jones on Unsplash

Before I get into the meat of the article, please sit for a lesson in how computers work:

Understood? Good.

For the red/green colourblind, let me explain. While a CPU is doing one thing, it can’t be doing another thing, which means you can’t sort a big array while a user scrolls the screen.

This is bad, if you have a big array and users with fingers.

Enter, Web Workers. These split open the atomic concept of a ‘CPU’ and allow us to think in terms of threads. We can use one thread to handle user-facing work like touch events and rendering the UI, and different threads to carry out all other work.

Check that out, the main thread is green the whole way through, ready to receive and respond to the gentle caress of a user.

You’re excited (I can tell), if we only have UI code on the main thread and all other code can go in a worker, things are going to be amazing (said the way Oprah would say it).

But cool your jets for just a moment, because websites are mostly about the UI — it’s why we have screens. And a lot of a user’s interactions with your site will be tapping on the screen, waiting for a response, reading, tapping, looking, reading, and so on.

So we can’t just say “here’s some JS that takes 20ms to run, chuck it on a thread”, we must think about where that execution time exists in the user’s world of tap, read, look, read, tap…

I like to boil this down to one specific question:

Is the user waiting anyway?

Imagine we have created some sort of git-repository-hosting website that shows all sorts of things about a repository. We have a cool feature called ‘issues’. A user can even click an ‘issues’ tab in our website to see a list of all issues relating to the repository. Groundbreaking!

When our users click this issues tab, the site is going to fetch the issue data, process it in some way — perhaps sort, or format dates, or work out which icon to show — then render the UI.

Inside the user’s computer, that’ll look exactly like this.

Look at that processing stage, locking up the main thread even though it has nothing to do with the UI! That’s terrible, in theory.

But think about what the human is actually doing at this point. They’re waiting for the common trio of network/process/render; just sittin’ around with less to do than the Bolivian Navy.

Because we care about our users, we show a loading indicator to let them know we’ve received their request and are working on it — putting the human in a ‘waiting’ state. Let’s add that to the diagram.

Now that we have a human in the picture, we can mix in a Web Worker and think about the impact it will have on their life:

Hmmm.

First thing to note is that we’re not doing anything in parallel. We need the data from the network before we process it, and we need to process the data before we can render the UI. The elapsed time doesn’t change.

(BTW, the time involved in moving data to a Web Worker and back is negligible: 1ms per 100 KB is a decent rule of thumb.)

So we can move work off the main thread and have a page that is responsive during that time, but to what end? If our user is sitting there looking at a spinner for 600ms, have we enriched their experience by having a responsive screen for the middle third?

No.

I’ve fudged these diagrams a little bit to make them the gorgeous specimens of graphic design that they are, but they’re not really to scale.

When responding to a user request, you’ll find that the network and DOM-manipulating part of any given task take much, much longer than the pure-JS data processing part.

I saw an article recently making the case that updating a Redux store was a good candidate for Web Workers because it’s not UI work (and non-UI work doesn’t belong on the main thread).

Chucking the data processing over to a worker thread sounds sensible, but the idea struck me as a little, umm, academic.

First, let’s split instances of ‘updating a store’ into two categories:

  1. Updating a store in response to a user interaction, then updating the UI in response to the data change
  2. Not that first one

If the first scenario, a user taps a button on the screen — perhaps to change the sort order of a list. The store updates, and this results in a re-rendering of the DOM (since that’s the point of a store).

Let me just delete one thing from the previous diagram:

In my experience, it is rare that the store-updating step goes beyond a few dozen milliseconds, and is generally followed by ten times that in DOM updating, layout, and paint. If I’ve got a site that’s taking longer than this, I’d be asking questions about why I have so much data in the browser and so much DOM, rather than on which thread I should do my processing.

So the question we’re faced with is the same one from above: the user tapped something on the screen, we’re going to work on that request for hopefully less than a second, why would we want to make the screen responsive during that time?

OK what about the second scenario, where a store update isn’t in response to a user interaction? Performing an auto-save, for example — there’s nothing more annoying than an app becoming unresponsive doing something you didn’t ask it to do.

Actually there’s heaps of things more annoying than that. Teens, for example.

Anyhoo, if you’re doing an auto-save and taking 100ms to process data client-side before sending it off to a server, then you should absolutely use a Web Worker.

In fact, any ‘background’ task that the user hasn’t asked for, or isn’t waiting for, is a good candidate for moving to a Web Worker.

The matter of value

Complexity is expensive, and implementing Web Workers ain’t cheap.

If you’re using a bundler — and you are — you’ll have a lot of reading to do, and probably npm packages to install. If you’ve got a create-react-app app, prepare to eject (and put aside two days twice a year to update 30 different packages when the next version of Babel/Redux/React/ESLint comes out).

Also, if you want to share anything fancier than plain data between a worker and the main thread you’ve got some more reading to do (comlink is your friend).

What I’m getting at is this: if the benefit is real, but minimal, then you’ve gotta ask if there’s something else you could spend a day or two on with a greater benefit to your users.

This thinking is true of everything, of course, but I’ve found that Web Workers have a particularly poor benefit-to-effort ratio.

Hey David, why you hate Web Workers so bad?

Good question.

This is a doweling jig:

I own a doweling jig. I love my doweling jig. If I need to drill a hole into the end of a piece of wood and ensure that it’s perfectly perpendicular to the surface, I use my doweling jig.

But I don’t use it to eat breakfast. For that I use a spoon.

Four years ago I was working on some fancy animations. They looked slick on a fast device, but janky on a slow one. So I wrote fireball-js, which executes a rudimentary performance benchmark on the user’s device and returns a score, allowing me to run my animations only on devices that would render them smoothly.

Where’s the best spot to run some CPU intensive code that the user didn’t request? On a different thread, of course. A Web Worker was the correct tool for the job.

Fast forward to 2019 and you’ll find me writing a routing algorithm for a mapping application. This requires parsing a big fat GeoJSON map into a collection of nodes and edges, to be used when a user asks for directions. The processing isn’t in response to a user request and the user isn’t waiting on it. And so, a Web Worker is the correct tool for the job.

It was only when doing this that it dawned on me: in the intervening quartet of years, I have seen exactly zero other instances where Web Workers would have improved the user experience.

Contrast this with a recent resurgence in Web Worker wonderment, and combine that contrast with the fact that I couldn’t think of anything else to write about, then concatenate that combined contrast with my contrarian character and you’ve got yourself a blog post telling you that maybe Web Workers are a teeny-tiny bit overhyped.

Thanks for reading

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Further reading

An Introduction to Web Workers

JavaScript Web Workers: A Beginner’s Guide

Using Web Workers to Real-time Processing

How to use Web Workers in Angular app

Using Web Workers with Angular CLI