Question

Prettier is an opinionated code formatter with support for:

• JavaScript, including ES2017
• JSX
• Angular
• Vue
• Flow
• TypeScript
• CSS, Less, and SCSS
• HTML
• JSON
• GraphQL
• Markdown, including GFM and MDX
• YAML

It removes all original styling* and ensures that all outputted code conforms to a consistent style. (See this blog post)

Prettier takes your code and reprints it from scratch by taking the line length into account.

For example, take the following code:

foo(arg1, arg2, arg3, arg4);

It fits in a single line so it's going to stay as is. However, we've all run into this situation:

foo(reallyLongArg(), omgSoManyParameters(), IShouldRefactorThis(), isThereSeriouslyAnotherOne());

Suddenly our previous format for calling function breaks down because this is too long. Prettier is going to do the painstaking work of reprinting it like that for you:

foo(
  reallyLongArg(),
  omgSoManyParameters(),
  IShouldRefactorThis(),
  isThereSeriouslyAnotherOne()
);

Prettier enforces a consistent code style (i.e. code formatting that won't affect the AST) across your entire codebase because it disregards the original styling* by parsing it away and re-printing the parsed AST with its own rules that take the maximum line length into account, wrapping code when necessary.

Footnotes

* Well actually, some original styling is preserved when practical—see empty lines and multi-line objects.