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Frontend Development

I've recently started learning how to make web frontends, two years ago I learned a bit of HTML, CSS, Javascript and React, but it didn't stick that much.

This time I'm full in with Vue which in my opinion is by far prettier than React.

Newbie tips

I feel completely lost xD, I don't know even how to search well what I need, it's like going back to programming 101. Funnily though, it's bringing me closer to the people I mentor on Python, I'm getting frustrated with similar things that they do, those things that you don't see when you already are proficient in a language, so here are some tips.

Don't resize your browser window

As I use i3wm, I've caught myself resizing the browser by adding terminals above and besides the browser to see how does the site react to different screen sizes. I needed the facepalm of a work colleague, which kindly suggested to spawn the Developer Tools and move that around. If you need to resize in the other direction, change the position of the Developer tools and grow it in that direction.

A better feature yet is to use the Responsive Design mode, which lets you select screen sizes of existent devices, and it's easy to resize the screen.

Your frontend probably doesn't talk to your backend

If you're using Vue or a similar framework, your frontend is just a webserver (like nginx) that has some html, js and css static files whose only purpose is to serve those static files to the user. It is the user's browser the one that does all the queries, even to the backend.

Imagine that we have a frontend application that uses a backend API behind the scenes. In the front application you'll do the queries on /api and depending on the environment two different things will happen:

  • In your development environment, when you run the development server to manually interact with it with the browser, you configure it so that whatever request you do to /api is redirected to the backend endpoint, which usually is listening on another port on localhost.

    If you are doing unit or integration tests, you'll probably use your test runner to intercept those calls and mock the result.

    If you are doing E2E tests, your test runner will probably understand your development configuration and forward the requests to the backend service.

  • In production you'll have an SSL proxy, for example linuxserver's swag, that will forward /api to the backend and the rest to the frontend.


Write testable code

Every test you write will include selectors for elements. To save yourself a lot of headaches, you should write selectors that are resilient to changes.

Oftentimes we see users run into problems targeting their elements because:

  • Your application may use dynamic classes or ID's that change.
  • Your selectors break from development changes to CSS styles or JS behavior.

Luckily, it is possible to avoid both of these problems.

  • Don't target elements based on CSS attributes such as: id, class, tag.
  • Don't target elements that may change their textContent.
  • Add data-* attributes to make it easier to target elements.

Given a button that we want to interact with:

  class="btn btn-large"

Let's investigate how we could target it: | Selector | Recommended | Notes | | cy.get('button').click() | Never | Worst - too generic, no context. | | cy.get('.btn.btn-large').click() | Never | Bad. Coupled to styling. Highly subject to change. | | cy.get('#main').click() | Sparingly | Better. But still coupled to styling or JS event listeners. | | cy.get('[name=submission]').click() | Sparingly | Coupled to the name attribute which has HTML semantics. | | cy.contains('Submit').click() | Depends | Much better. But still coupled to text content that may change. | | cy.get('[data-cy=submit]').click() | Always | Best. Isolated from all changes. |

Conditional testing

Conditional testing refers to the common programming pattern:

If X, then Y, else Z

Here are some examples:

The problem is - while first appearing simple, writing tests in this fashion often leads to flaky tests, random failures, and difficult to track down edge cases.

Some interesting cases and their solutions:

Last update: 2022-04-24