Reprint

Takes in an AST and pretty prints it.

(function foo(someLongArgument, anotherLongArgument,
   aThirdReallyLongArgumentNameThatCouldBreakThings) { dosomething()})(1, 2, 3);

(function bar(
  a,
  b,
  c
){})();

Becomes:

(function foo(
  someLongArgument,
  anotherLongArgument,
  aThirdReallyLongArgumentNameThatCouldBreakThings,
) {
  dosomething();
})(1, 2, 3);

(function bar(a, b, c) {})();

Ideology

This only reprints the existing AST, it should not result in a change that alters the AST in any way. Fixing the AST is the job of another tool.

We do:

• Add trailing commas
• Add parens around the single argument in an arrow function

We don't:

• Separate long string literals with + so the line can break
  • May be worth doing this since it almost has to be done within a formatter, it doesn't make much sense for this to be done as a transform with no context of how the code will be printed.
• Switch the type of quotes around string literals
  • This can change how things must be escaped
  • Could potentially fix this by not considering literal.raw part of the AST, but literal.raw is required in order to print integral number literals that exceed MAX_SAFE_INTEGER
• Simplify unnecessary parenthesis around series of expressions

Code Patterns and Terminology

Simple

Simple means that no context is needed in order to produce the output. Nodes below the tree rooted at the current node are not considered additional context.

Complex

Complex means that context is required to produce the output. This means nodes above, or siblings of the current node are required.

Printer

A printer takes in a node and any context in order to produce an array of lines.

Wrapper

A wrapper is similar to a printer except that it also takes in some already printed lines.

Resolver

A resolver works on lines and options (not the full context) in order to remove markers.

Marker

A marker is a special string that conveys some information to a resolver. It may tell the resolver to add a space, or that it's okay to break at the current location.