Parsing and processing DOM nodes in a non-blocking way using CPS technique.

cps_demo.js

function traverse(node, processTask, continuation) {
  processTask(node, function handleChildren() {
    const children = node.childNodes;

    function handleOne(i, len, continuation) {
      if (i < len) {
        traverse(children[i], processTask, function handleNext() {
          handleOne(i + 1, len, continuation);
        });
      } else {
        continuation();
      }
    }

    handleOne(0, children.length, continuation);
  });
}

const stats = {};

function histogram(node, continuation) {
  if (node.nodeType === 3) {
    node.nodeValue.replace(/\w+/g, function (match) {
      stats[match] = stats[match] ? stats[match] + 1 : 1;
      return match;
    });
  }

  if (histogram.skip++ % 400 === 0) {
    setTimeout(continuation, 0);
  } else {
    continuation();
  }
}
histogram.skip = 0;

function show(continuation) {
  function handleOne(i, keys, continuation) {
    if (i < keys.length) {
      const key = keys[i];
      console.log(`${key}: ${stats[key]}`);

      if (i % 20 === 0) {
        setTimeout(function () {
          handleOne(i + 1, keys, continuation);
        }, 0);
      } else {
        handleOne(i + 1, keys, continuation);
      }
    } else {
      continuation();
    }
  }

  handleOne(0, Object.keys(stats), continuation);
}

function end() {
  console.log('done');
}

traverse(document.body, histogram, function () {
  show(end);
});