Dummy source node map, with reduction over non-word tokens.

01_reduce.js

  SourceMapConcatHelper.prototype._dummyNode = function(src, name) {
    var node = new SourceNode();
    var lineIndex = 1;
    var charIndex = 0;
    // Tokenize on words, new lines, and white space.
    var tokens = src.split(/(\n|\b)/g);
    // Filter out empty strings.
    tokens = tokens.filter(function(t) { return !!t; });
    // Reduce whitespace tokens together.
    tokens = tokens.reduce(function(dest, t, index, src) {
      var lastTokenIsNotWord =
        dest.length && /^\W+$/.test(dest[dest.length - 1]);
      var tokenIsNotWord = /^\W+$/.test(t);
      var nextTokenIsNotWord = /^\W+$/.test(src[index + 1]);
      var secondLastTokenIsNotWord =
        dest.length >= 2 && /^\W+$/.test(dest[dest.length - 2]);
      if (
        lastTokenIsNotWord && tokenIsNotWord && (
          t !== '\n' && nextTokenIsNotWord ||
          t === '\n' && secondLastTokenIsNotWord
        )
      ) {
        dest[dest.length - 1] += t;
      } else {
        dest.push(t);
      }
      return dest;
    }, []);

    tokens.forEach(function(token) {
      node.add(new SourceNode(lineIndex, charIndex, name, token));
      if (token[token.length - 1] === '\n') {
        lineIndex++;
        charIndex = 0;
      } else {
        charIndex += token.length;
      }
    });

    return node;
  };

02_drop_whitespace.js

  SourceMapConcatHelper.prototype._dummyNode = function(src, name) {
    var node = new SourceNode();
    var lineIndex = 1;
    var charIndex = 0;
    // Tokenize on words, new lines, and white space.
    var tokens = src.split(/(\n|[^\S\n]+|\b)/g);
    // Filter out empty strings.
    tokens = tokens.filter(function(t) { return !!t; });

    tokens.forEach(function(token) {
      // If the token contains a non-whitespace or newline character, add it.
      if (/[\S\n]/.test(token)) {
        node.add(new SourceNode(lineIndex, charIndex, name, token));
      }
      if (token[token.length - 1] === '\n') {
        lineIndex++;
        charIndex = 0;
      } else {
        charIndex += token.length;
      }
    });

    return node;
  };