How to trigger selection event

GoJS
2

The default behavior is that when the user clicks on a GraphObject, that object’s GraphObject.part will be selected. That’s the simple case, and it’s all controlled by ClickSelectingTool. Here’s how it handles the mouse-up of a click:

ClickSelectingTool.prototype.doMouseUp = function() {
  if (this.isActive) {
    this.standardMouseSelect();
    var handled = this.standardMouseClick();
    if (!handled) {
      if (this.diagram !== null && this.diagram.lastInput.isTouchEvent) {
        this.diagram.toolManager.doToolTip();
      }
    }
  }
  this.stopTool();
};

So you might want to either override this method or ClickSelectingTool.standardMouseSelect. FYI, that is defined as:

Tool.prototype.standardMouseSelect = function() {
  var diagram = this.diagram;
  if (diagram === null || !diagram.allowSelect) return;
  var e = diagram.lastInput;
  var curobj = diagram.findPartAt(e.documentPoint, false);  // to select containing Group if Part.canSelect() is false
  if (curobj !== null) {
    if (e.meta || e.control) {  // toggle the part's selection
      diagram.raiseDiagramEvent('ChangingSelection');
      var part = curobj;
      while (part !== null && !part.canSelect()) part = part.containingGroup;
      if (part !== null) part.isSelected = !part.isSelected;
      diagram.raiseDiagramEvent('ChangedSelection');
    } else if (e.shift) {  // add the part to the selection
      if (!curobj.isSelected) {
        diagram.raiseDiagramEvent('ChangingSelection');
        var part = curobj;
        while (part !== null && !part.canSelect()) part = part.containingGroup;
        if (part !== null) part.isSelected = true;
        diagram.raiseDiagramEvent('ChangedSelection');
      }
    } else {
      if (!curobj.isSelected) {
        var part = curobj;
        while (part !== null && !part.canSelect()) part = part.containingGroup;
        if (part !== null) diagram.select(part);  // also raises ChangingSelection/Finished
      }
    }
  } else if (e.left && !(e.meta || e.control) && !e.shift) {
    // left click on background with no modifier: clear selection
    diagram.clearSelection();  // also raises ChangingSelection/Finished
  }
};