dvMinifyJs function

String dvMinifyJs(String js)

js without its comments and without the indentation, and with every line it had.

Lines are never joined. JavaScript inserts semicolons at newlines, so const a = 1 followed by const b = 2 is two statements on two lines and one syntax error on one. Nothing inside a string, a template literal or a regular expression is touched.

Implementation

String dvMinifyJs(String js) {
  final StringBuffer out = StringBuffer();
  bool space = false;
  bool newline = false;
  // What was written last decides whether the next `/` opens a regular
  // expression or divides: `return /x/` is a pattern, `a / x` is division.
  String previous = '';

  void flush() {
    if (out.isEmpty) return;
    if (newline) {
      out.write('\n');
    } else if (space) {
      out.write(' ');
    }
    space = false;
    newline = false;
  }

  void write(String text) {
    flush();
    out.write(text);
    previous = text.trimRight();
    space = false;
    newline = false;
  }

  for (int i = 0; i < js.length; i++) {
    final String c = js[i];

    if (c == '/' && i + 1 < js.length && js[i + 1] == '/') {
      final int end = js.indexOf('\n', i);
      i = end < 0 ? js.length : end - 1;
      space = true;
      continue;
    }
    if (c == '/' && i + 1 < js.length && js[i + 1] == '*') {
      final int end = js.indexOf('*/', i + 2);
      final String comment = js.substring(i, end < 0 ? js.length : end + 2);
      if (comment.contains('\n')) newline = true;
      space = true;
      i = end < 0 ? js.length : end + 1;
      continue;
    }
    if (c == '\n') {
      newline = true;
      space = true;
      continue;
    }
    if (_isSpace(c)) {
      space = true;
      continue;
    }
    if (c == '"' || c == "'") {
      final int end = _stringEnd(js, i, c);
      write(js.substring(i, end));
      i = end - 1;
      continue;
    }
    if (c == '`') {
      final int end = _templateEnd(js, i);
      write(js.substring(i, end));
      i = end - 1;
      continue;
    }
    if (c == '/' && _regexCanStart(previous)) {
      final int end = _regexEnd(js, i);
      write(js.substring(i, end));
      i = end - 1;
      continue;
    }
    write(c);
  }
  return out.toString();
}