What steps can I take to perform unit testing on a custom element?

While working on a project where I have a class that extends HTMLElement, I came across some interesting information in this discussion:

https://github.com/Microsoft/TypeScript/issues/574#issuecomment-231683089

I discovered that I was unable to create an instance of a custom element without encountering an "Illegal constructor" error. Furthermore, the registerElement method seemed like a solution as it provided the constructor for the custom element, but it has been deprecated in favor of using CustomElementRegistry.define(). This new method exists on the window object and returns void. Any help or suggestions would be greatly appreciated.

In my specific case, I am choosing to utilize native custom elements instead of a web component framework since I only require custom elements. Additionally, I am working with TypeScript and attempting to incorporate Jest for testing purposes.

Answer №1

When considering the functionality of your element, it may be beneficial to incorporate the principles of "separation of concern" and "inversion of control."

Implementing different aspects of your element in separate classes helps achieve separation of concern. This allows for easier testing without needing to instantiate a concrete HtmlElement.

By utilizing inversion of control, you can set dependencies of separated classes (such as HtmlElement) from outside the class. This makes it simple to stub or mock the HtmlElement for testing purposes.

The goal is to structure your code in a way that is not reliant on external factors that are difficult to access or control during unit testing.

Similar questions

If you have not found the answer to your question or you are interested in this topic, then look at other similar questions below or use the search

Combining Array Elements to Create a Unified Object with Vue

Is there a way to transform an array into a list of objects? Transform [ { "currenttime":43481.46983805556, "moped":"30 minutes", "car":"1 hour" } ] to { "currenttime":43481.46983805556, "moped":"30 minutes", ...

Phone Validation for Contact Form 7

Recently, I was tasked with creating a landing page for a job interview. The challenge was to include validation on the phone number field so that it has to be between 9 and 10 numbers in length, along with another validation requiring the phone number t ...

I am looking to present a nested array within an array in a tabular format

This is the structure of my database: [{ "firstName": "Shaun", "salary": [ { "id":1, "rate": 250, }, { "id":2, "rate": 290, } ] },{ "firstName": "Julian", "salary": [ { "id":1, "rate": 750, ...

Why won't applying a binding style affect the appearance of my Vue component?

const EventLevelBoard = { name: "EventLevel", data: { levelStyle: { display: "block" }, levelStyleinner: [ { display: "block" }, { display: "block" }, { display: "block&qu ...

Using React to access the properties of objects within an array that has been dynamically mapped

For my initial dive into developing a React application, I am currently in the process of fetching data from a database and updating the state to store this information as an array. My main challenge lies in accessing the properties of the objects within t ...

Unexpected behavior observed in JavaScript and AJAX functionality

In my web development project, I've decided to incorporate JavaScript and AJAX for the signup form functionality. However, I seem to be facing some challenges as I try to post all the textbox values from the signup form through AJAX. The code snippe ...

Error: The function $compile does not exist

Currently, I am working on developing an AngularJS directive using TypeScript. While testing my code in the browser, I encountered the following error: TypeError: $compile is not a function at compileComponent.js:14 Interestingly, the TypeScript compiler ...

What is the best way to extract specific data from a JSON file based on a chosen property using AngularJS and the $http.get method?

I am working with a JSON file that contains color information like this: { "colorsArray":[{ "colorName":"red", "hexValue":"#f00" }, { "colorName":"green", "hexValue":"#0f0" }, { "colorName":"blue", "hexValue":"#00f" }, ...

Type of result from a function that returns a linked promise

In my class, I have a method that returns a chained promise. The first promise's type is angular.IPromise<Foo>, and the second promise resolves with type angular.IPromise<Bar>. I am perplexed as to why the return type of doSomething is an ...

Error: Promises must be managed correctly

I've been working on a timer-based function that is supposed to run once a week and create almost identical copies of existing documents. However, every time I try to execute it, I encounter the error message "Promises must be handled appropriately." ...

What approach does JavaScript take when encountering a value that is undefined?

Having recently delved into JavaScript and exploring a book, I came across an interesting example in the recursive chapter: function findSolution(target) { function find(current, history) { if (current == target) return history; else if (c ...

Utilize JQuery's .load() function to transmit JSON data to your Flask server

I am attempting to utilize JQuery's .load() function in order to transmit data to my Flask server and then, with that information, display a <div> that is loaded into the element making the request. This is what my code snippet looks like: $(&qu ...

Discover the power of debugging Typescript in Visual Studio Code with Gulp integration

I've been working on setting up an express/typescript/gulp application, and while it's functional, I'm struggling to debug it using source-maps. Here is how I've set it up: Gulp File var gulp = require('gulp'), nodemon ...

Utilizing the power of JavaScript/JQuery to showcase a compilation of all input values within an HTML form

I'm struggling to showcase all the input values from my HTML form on the final page before hitting the "submit" button. Unfortunately, I am facing a challenge as the values are not appearing on the page as expected. Despite several attempts, the valu ...

Embedding image URLs fetched from JSON data within <li> elements

I have successfully retrieved a JSON response, which is displayed using the code below: Within my HTML document, I have the following structure: <ol id="selectable"></ol> In my JavaScript code, I make use of the following: <script type=" ...

What steps can I take to resolve the CLIENT_MISSING_INTENTS issue?

After diving into learning about discord.js, I've run into a bit of a roadblock. Despite trying to troubleshoot by searching online, I can't seem to resolve the issue. const Discord = require('discord.js'); // const Discord = require(&a ...

Searching through an array of objects in MongoDB can be accomplished by using the appropriate query

Consider the MongoDB collection 'users' with the following document: { _id: 1, name: { first: 'John', last: 'Backus' }, birth: new Date('Dec 03, 1924'), death: new Date('Mar 1 ...

The term 'Employee' is typically used as a classification, but in this context, it is being treated as a specific value

I am encountering an issue while trying to define a variable as type Employee. The error message 'Employee' only refers to a type but is being used as a value here. ts(2693) keeps appearing. Here is my show-api.ts code: import { Component, OnIni ...

The setInterval function does not function properly in IE8 when set to 0

I have a function called changeColor that updates the styling of certain elements in my HTML. In order to apply this function, I am using a timer like so: var timer = setInterval(changeColor,0); The issue I am encountering is that setting the time interv ...

Is it possible to incorporate FCM into Next.js and effectively handle server-side events for FCM on Next.js servers?

Is it feasible to incorporate the Firebase Cloud Messaging (FCM) into my upcoming Next.js application? Can I manage both client-side and server-side modules within the server side? ...