index.js

#!/usr/bin/env node

/*
 * See also:
 * https://docs.npmjs.com/misc/coding-style#semicolons
 * Switch statement semicolons should be ok to replace with line breaks.
 */

'use strict'

var _ = require('lodash')
var rocambole = require('rocambole')

var NEED_PREFIX_AT_START_OF_LINE = ['(', '[', '-', '+']

module.exports = function (src) {
  return rocambole.moonwalk(src, function (node) {
    var token = node.endToken

    // semicolons inside a for loop don't seem to pop up as tokens

    if (token.type !== 'Punctuator') return
    if (token.value !== ';') return

    if(node.parent && node.parent.type === `ForStatement`) {
      return
    }

    if(token._keep) {
      return
    }

    if(node.type === 'ForStatement') {
      token._keep = true
    }

    if (node.type === 'WhileStatement'
      || node.type === 'ForStatement'
      || node.type === 'EmptyStatement'
      || node.type === 'IfStatement'
    ) {
      return
    }

    if (token.next && token.next.type === 'WhiteSpace') {
      if(token.next.next
        && token.next.next.value != '}'
        && token.next.next.type != 'LineComment'
      ) {
        token.next.value = ''
      }
    }

    var prevToken = _findPrevNonWhiteSpace(token)
    var nextToken = _findNextNonWhiteSpace(token)

    if (!prevToken && !nextToken) {
      token.value = ''
      return
    }

    if (!prevToken || prevToken.type === 'LineBreak') {
      if(nextToken.type === 'RegularExpression') return
      if (~NEED_PREFIX_AT_START_OF_LINE.indexOf(nextToken.value)) {
        return
      }
      token.value = ''
      return
    }

    if (!nextToken) {
      token.value = ''
      return
    }

    if (nextToken.type === 'LineComment' || nextToken.type === 'LineBreak' || nextToken.value === '}') {
      token.value = ''
      return
    }

    var indentation = _findIndentation(token)

    if (indentation) {
      insertIndentationAfter(token, indentation)
    }

    token.type = 'LineBreak'
    token.value = '\n'
  })
}

function insertIndentationAfter (token, indentation) {
  var newIndentation = {}
  _.extend(newIndentation, indentation,
    {
      prev: token,
      next: token.next
    }
  )
  token.next.prev = newIndentation
  token.next = newIndentation
}

function _findNextNonWhiteSpace (token) {
  while (token.next) {
    token = token.next
    if (token.type !== 'WhiteSpace') return token
  }
}

function _findPrevNonWhiteSpace (token) {
  while (token.prev) {
    token = token.prev
    if (token.type !== 'WhiteSpace') return token
  }
}

function _findIndentation (token) {
  var indentation
  while (token.prev) {
    token = token.prev
    if (token.type === 'WhiteSpace') {
      indentation = token
      continue
    }
    if (token.type === 'LineBreak') {
      return indentation
    }
    indentation = undefined
  }

  return indentation
}