ECMAScript code indenter based on Esprima AST and Rocambole


ECMAScript code indenter based on Esprima AST

work in progress

This project started as an experiment while trying to decouple the indent logic from the other token manipulations on esformatter. It's an attempt at finding a simpler solution to the problem while still maintaining the flexibility.

By building it as a separate tool it is also simpler to reuse it for other projects and will make some of the tests simpler to write (since we can test the indentation separately).

This tool uses a rocambole generated AST to traverse tokens inside each node and add/remove indent based on the node type.

The algorithm is very straightforward, it simple loops through all nodes (starting from the leaf) up to the program root, scanning each line start for WhiteSpace and adding/removing/editing Indent tokens as needed.

  • Indent based on syntax (not tokens).
  • Options to toggle behavior.
  • Be able to indent any JavaScript program!

Transforms AST in-place, adding Indent tokens at the beginning of each line that needs indentation.

var esi = require('esindent');
esi.transform(ast, {
  value: '  ',
  ArrayExpression: 1,
  BlockStatement: 1,
  ChainedMemberExpression: 1,
  MultipleVariableDeclaration: 1,
  ObjectExpression: 1,
  SwitchCase: 1,
  SwitchStatement: 1,
  EmptyStatement: 0
// to get the result as a string simply call ast.toString() 
console.log( ast.toString() );

Released under the MIT License