ArgumentSplitter.js

class ArgumentSplitter {
  static split(argumentString) {
    return (new this(argumentString)).parse().arguments
  }

  constructor(argumentString) {
    this.argumentString = argumentString
    this.arguments      = null
  }

  get length() {
    return this.arguments === null ? null : this.arguments.length
  }

  parse() {
    this.pos             = 0
    this.arguments       = []
    this.currentArgument = ""

    this.readUntilArgument()
    while(this.pos < this.argumentString.length) {
      switch(this.argumentString[this.pos]) {
        case '"': this.readDoubleQuotedSubstring(); break
        case "'": this.readSingleQuotedSubstring(); break
        case " ": case "\t": case "\r": case "\n":
          this.terminateArgument(); break
        default:  this.readBareword()
      }
    }
    this.terminateArgument()

    this.currentArgument = null
    this.pos             = null

    return this
  }

  terminateArgument() {
    if (this.currentArgument.length > 0) {
      this.arguments.push(this.currentArgument)
      this.currentArgument = ""
    }
    this.pos++
  }

  readBareword() {
    var terminated = false

    while(!terminated && this.pos < this.argumentString.length) {
      switch(this.argumentString[this.pos]) {
        case " ": case "\t": case "\r": case "\n":
        case '"': case "'":
          terminated = true
          this.pos--
          break
        case '\\':
          this.pos++
        default:
          this.currentArgument += this.argumentString[this.pos]
      }
      this.pos++
    }
  }

  readDoubleQuotedSubstring() {
    var terminated = false

    this.pos++ // move beyond starting quote
    while(!terminated && this.pos < this.argumentString.length) {
      switch(this.argumentString[this.pos]) {
        case '"':  terminated = true; break
        case '\\': this.pos++
        default:   this.currentArgument += this.argumentString[this.pos]
      }
      this.pos++
    }
  }

  readSingleQuotedSubstring() {
    var terminated = false

    this.pos++ // move beyond starting quote
    while(!terminated && this.pos < this.argumentString.length) {
      switch(this.argumentString[this.pos]) {
        case "'":  terminated = true; break
        case '\\': this.pos++
        default:   this.currentArgument += this.argumentString[this.pos]
      }
      this.pos++
    }
  }

  readUntilArgument() {
    while(this.pos < this.argumentString.length) {
      switch(this.argumentString[this.pos]) {
        case ' ':
        case '\t':
        case '\r':
        case '\n':
          this.pos++
        default:
          return
      }
    }
  }
}