Function addChangeToHistory

src/codemirror.js:7951–7991

(doc, change, selAfter, opId)

  // a single operation, ore are close together with an origin that
  // allows merging (starting with "+") into a single event.
  function addChangeToHistory(doc, change, selAfter, opId) {
    var hist = doc.history;
    hist.undone.length = 0;
    var time = +new Date, cur;

    if ((hist.lastOp == opId ||
         hist.lastOrigin == change.origin && change.origin &&
         ((change.origin.charAt(0) == "+" && doc.cm && hist.lastModTime > time - doc.cm.options.historyEventDelay) ||
          change.origin.charAt(0) == "*")) &&
        (cur = lastChangeEvent(hist, hist.lastOp == opId))) {
      // Merge this change into the last event
      var last = lst(cur.changes);
      if (cmp(change.from, change.to) == 0 && cmp(change.from, last.to) == 0) {
        // Optimized case for simple insertion -- don't want to add
        // new changesets for every character typed
        last.to = changeEnd(change);
      } else {
        // Add new sub-event
        cur.changes.push(historyChangeFromChange(doc, change));
      }
    } else {
      // Can not be merged, start a new event.
      var before = lst(hist.done);
      if (!before || !before.ranges)
        pushSelectionToHistory(doc.sel, hist.done);
      cur = {changes: [historyChangeFromChange(doc, change)],
             generation: hist.generation};
      hist.done.push(cur);
      while (hist.done.length > hist.undoDepth) {
        hist.done.shift();
        if (!hist.done[0].ranges) hist.done.shift();
      }
    }
    hist.done.push(selAfter);
    hist.generation = ++hist.maxGeneration;
    hist.lastModTime = hist.lastSelTime = time;
    hist.lastOp = hist.lastSelOp = opId;
    hist.lastOrigin = hist.lastSelOrigin = change.origin;

    if (!last) signal(doc, "historyAdded");
  }

  function selectionEventCanBeMerged(doc, origin, prev, sel) {
    var ch = origin.charAt(0);