hand-rolled query parser

parse.js

function parse(query) {
  var curTerm = null
  var curPhrase = null
  var curKey = null
  var result = []
  for (var char of query) {
    switch (char) {
    case '"':
      if (curPhrase != null) {
        if (curKey) {
          // close keyword value phrase
          result.push({ type: 'keyword', key: curKey, phrase: curPhrase })
          curKey = null
        } else {
          // close normal phrase
          result.push({ type: 'phrase', phrase: curPhrase })
        }
        curPhrase = null
      } else {
        if (curTerm != null) {
          // phrase begins in the middle of a word
          // use the first half of the word as a normal term
          result.push({ type: 'term', value: curTerm })
          curTerm = null
        }
        // open new phrase
        curPhrase = ''
      }
      break
    case ':':
      if (curPhrase != null) {
        // add to open phrase
        curPhrase += char
      } else if (curTerm != null) {
        // curTerm is a keyword key
        curKey = curTerm
        curTerm = null
      } else {
        // a `:` preceeded by whitespace is meaningless
      }
      break
    case ' ':
    case '\n':
    case '\t':
      if (curPhrase != null) {
        // add whitespace to an open phrase
        curPhrase += char
      } else if (curKey != null) {
        // if building a keyword
        if (curTerm != null) {
          // use the current term as the value
          result.push({ type: 'keyword', key: curKey, value: curTerm })
        } else {
          // with no value, treat the key as a normal term
          result.push({ type: 'term', value: curKey })
        }
        curTerm = null
        curKey = null
      } else if (curTerm != null) {
        // terms are separated by whitespace
        result.push({ type: 'term', value: curTerm })
        curTerm = null
      }
      break
    default:
      if (curPhrase != null) {
        // if a phrase is open, add to it
        curPhrase += char
      } else if (curTerm != null) {
        // if a term is present, add to it
        curTerm += char
      } else {
        // this is the start of a new term
        curTerm = char
      }
      break
    }
  }
  if (curKey) {
    if (curPhrase) {
      // keyword with unfinished phrase value
      result.push({ type: 'keyword', key: curKey, phrase: curPhrase })
    } else if (curTerm) {
      // keyword with normal term value
      result.push({ type: 'keyword', key: curKey, value: curTerm })
    } else {
      // keyword with no value, use as normal term
      result.push({ type: 'term', value: curKey })
    }
  } else if (curPhrase) {
    // unclosed phrase
    result.push({ type: 'phrase', value: curPhrase })
  } else if (curTerm) {
    // trailing term
    result.push({ type: 'term', value: curTerm })
  }
  return result
}

console.log(parse('one two'))
console.log(parse('"a phrase" term'))
console.log(parse('"a  phrase" term "broken phrase'))
console.log(parse('term by:me "a phrase"'))
console.log(parse('by:"keyword phrase" three'))
console.log(parse('one by: me two :me by:"keyword phrase" three'))
console.log(parse('quote"in the middle'))