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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!


esindent.transform(ast[, opts]):AST

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

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


Remove WhiteSpace tokens that are at the beginning of the lines (probably from original indent or trailing white spaces). Also remove Indent tokens that doesn't have the level property or that are not preceded by a line break.


Set the indent options. Useful for cases where you want to use transformNode() or call transform() multiple times in a row (so you don't need to set the options multiple times). - Used internally by esindent.transform().


Released under the MIT License