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Pretty and the JS

Pavlin Gergov
Oct 23, 2017
We’re going to talk about JavaScript, Prettier and consistent code style & formatting


As programmers, part of our daily job is writing clean, simple, and readable code. Writing a program is a lot like writing an essay – your message is more convincing when it’s accompanied by proper grammar and punctuation. When you’re programming you should follow the same principle because of two reasons. One day you might be assigned to work with other people and support your (and their) code for long periods of time. Or even better – you’ll have to read, understand and maintain someone else’s code!

So what programming principles are we talking about?

  • Keep programs and methods short and manageable
  • Use language-specific idioms
  • Use straightforward logic and flow-of-control
  • Avoid magic numbers; instead, give them meaningful symbolic names
  • Use meaningful names for … pretty much everything

Talking about pretty much everything – you should also check your spelling. And by saying that I don’t mean go get a spelling dictionary, but rather follow code and style guides of the language you’re using. In some cases this is easier said than done and this article is going to cover one specific case.


Yes, the good old JavaScript. Old but gold. At this moment we have ECMAScript 2017, JSX, TypeScript, and many more supersets that all transpile to JavaScript. All of them are great, each gives us nifty functionalities, but as we already said – in some future point of time we’ll have to read & support what we’ve written. And that’s exactly what happened in my team.

A new project was started, we were very happy and enthusiastic, sprints were crushed and a few weeks later it was time to refactor (yes, we’re one of those teams that do that). As a result, we ended up with simpler and better code, but in the making, we had one big problem – everyone had a different understanding of code formatting (how to arrange function arguments, when to break new lines, usage of single and double quotes, etc.) and we struggled to unify the format all around.

Solution? Prettier! There’s no reason for anyone to spend any time and mental energy formatting their (and his teammates’) code.

What is prettier

Prettier is a JavaScript formatter with advanced support for language features from ES2017, JSX, and Flow. Prettier gets rid of all original styling and guarantees consistency by parsing JavaScript into an AST (abstract syntax tree) and pretty-printing the AST. Unlike eslint, there aren’t a million configuration options and rules. But more importantly: everything is fixable. Kudos to James Long for his great work!

Adding prettier to your project

There are a few ways to introduce prettier in your project.

First steps

The easiest one is adding integration to your favourite text editor. Most common editors already have a package written, but if you don’t find yours in the list feel free to develop one and add it here. Next step would be adding some options that differ from default ones. Then all of your current (and future) teammates will have to do this. Something smells fishy. I see repeatable action with a lot of room for errors (everyone has their own prettier settings).

We can do better

To avoid PRs (pull requests) with 10 lines of new logic and 150 lines changed because of different settings in your colleague’s editor we can write a simple bash script (bear with me, I also get scared every time I hear/see bash) that will prettify all files you’ve changed before committing them:

# Apply prettier to all changed (staged or unstaged) files

git diff \
    --name-only HEAD \
    | grep '\.js\|\.jsx\|\.ts\|\.<any-other-extension-you-need>\?$' \
    | xargs <path-to-your-prettier-executable> \
            --write \
            --print-width 80 \
            --tab-width 2 \

Something to note here is the --write option. By using it one allows prettier to edit files directly! Without it, you’ll end up with pretty code pasted in the terminal. To avoid explicitly specifying all settings in every bash file you use prettier you can add .prettierrc file (or symlink) in JSON or YAML format in the folder from which the bash script is being executed. I like to have control over everything I do, but if you prefer you can add a pre-commit hook that runs the script when you do git add.

With .prettierrc in place, most editors will find the settings and use them, but sadly we don’t live in a perfect world and our editor might be messed up or it’s one of those days when the coffee kicks up with a delay and somehow we push code that’s not prettier formatted.

Even betterer

What can we do about the problem above? Write another bash script of course. This time we’re going to execute it on our favourite CI (continuous integration) and make prettier part of our frontend tests. What we want to achieve is run prettier on every file that’s supposed to be formatted and assert it’s pretty:



for file in $(find <your-source-folder> -name '*.js' -o -name '*.<another-extension>'); do

  [ -f "$file" ] || continue

  <path-to-prettier> \
            "$file" \
            > "$TEMP"
  diff "$TEMP" "$file" > /dev/null 2>&1

  if  [ "$LAST_STATUS" -ne 0 ]
    echo "$file is not pretty."


rm "$TEMP"
exit "$EXIT_CODE"

This time instead of having --write we save the output in temporary file which we compare to the original (commited) one. With this step we just unified the code style of our project.


If you’re also looking for a proper grammar and punctuation tool for your JavaScript project give Prettier a try and never worry about formatting.

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