Prettier

A wrapper for the Prettier code formatter written in Swift. The package runs the code formatter in Apple's JavaScriptCore. All the necessary JavaScript files are bundled with this package.

Can this package be used in production?

Probably. The package uses stable versions of all dependencies and I intend to use it in one of my upcoming projects. Use it at your own risk though.

Installation

Prettier is distributed using the Swift Package Manager. Install it in your project by adding it as a dependency in your Package.swift manifest or through "Package Dependencies" in your project settings.

let package = Package(
    dependencies: [
        .package(url: "git@github.com:simonbs/Prettier.git", from: "0.1.0")
    ]
)

Usage

To get started with Prettier you must first import the module.

import Prettier

Now you can create an instance of PrettierFormatter.

let formatter = PrettierFormatter(plugins: [BabelPlugin()], parser: BabelParser())

We need to pass the plugins to use with Prettier. Some documents can be formatted with a single plugin and some may require multiple parsers if the document includes a mix of languages. An example of this is HTML documents that may contain HTML, CSS and JavaScript.

Next we're passing the parser to use to use for formatting the code.

To format HTML we would create our PrettierFormatter as shown below.

let formatter = PrettierFormatter(plugins: [HTMLPlugin(), PostCSSPlugin(), BabelPlugin()] , parser: HTMLParser())

See the Supported Languages for a list of all plugins and parsers.

After creating an instance of PrettierFormatter, you must prepare the formatter before formatting code.

formatter.prepare()

This prepares the instance by loading the bundled JavaScript files from disk and evaluating them in JavaScriptCore. It is recommended to do this as early as possible so you're ready to format the code later.

With the PrettierFormatter instance prepared you can start formatting code.

// 💩 This is some poorly formatted JavaScript that we'll format.
let script = """
if(hello=="world"){
return"Hello world"
}
"""
// Earlier we have created and prepared our instance of Prettier. We're ready to format the JavaScript code.
let result = formatter.format(script)
switch result {
case .success(let formattedCode):
    print(formattedCode)
    // ✨ Here's our formatted code. Looks great!
    // if (hello == "world") {
    //   return "Hello world";
    // }
case .failure(let error):
    // Perform proper error handling.
    print(error)
}

It's possible to format only a specific range in the input string by calling -format(:limitedTo:).

let result = formatter.format(script, limitedTo: 20 ... 39)
switch result {
case .success(let formattedCode):
    break
case .failure(let error):
    // Perform proper error handling.
    print(error)
}

You can also specify a location to be translated from the unformatted code to the formatted code. This is useful for moving the cursor when developing a text editor.

let result = formatter.format(script, withCursorAtLocation: 38)
switch result {
case .success(let formatResult):
    print(formatResult.formattedString)
    print(formatResult.cursorOffset)
case .failure(let error):
    // Perform proper error handling.
    print(error)
}

Note that the result returned by -format(:withCursorAtLocation:) is different that the result returned from both -format() and -format(:limitedTo:) because this one contains the location in the formatted string.

There are several properties that can be used to tweak the formatted code. These options map 1:1 to options in the JavaScript implementation of Prettier. For more information on the options, please have a look at PrettierFormatter.swift as well as the documentation for the JavaScript implementation of Prettier.

Supported Languages

This package bundles the Prettier library along with support for the following languages and frameworks. The table below shows the language name and the parser to be used in order to format code in that language. A parser can support more languages.

Package	Parsers
PrettierBabel	BabelFlowParser, BabelParser, BabelTSParser, JSON5Parser, JSONParser, JSONStringifyParser	BabelParser can be used for parsing JavaScript.
PrettierEspree	EspreeParser
PrettierFlow	FlowParser
PrettierGlimmer	GlimmerParser	Used for Handlebars.
PrettierGraphQL	GraphQLParser
PrettierHTML	AngularParser, HTMLParser, LWCParser, VueParser	Include BabelParser and CSSParser to parse entire HTML documents. HTMLParser can be used to parse Vue.
PrettierMarkdown	MarkdownParser, MDXParser
PrettierMeriyah	MeriyahParser
PrettierPHP	PHPParser
PrettierPostCSS	CSSParser, LessParser, SCSSParser
PrettierTypeScript	TypeScriptParser
PrettierYAML	YAMLParser

Acknowledgements

The package uses the following dependencies.

• prettier/prettier
• prettier/plugin-php

License

MIT