onBeforeUndo

fires before the undo() method is called

boolean onBeforeUndo(array action);

action

array

an array of command objects

boolean

defines whether the default action of the event will be triggered (true) or canceled (false)

gantt.attachEvent("onBeforeUndo", function(action){
    // your code here
    return true;
});

Details

This event is defined in the undo extension, so you need to activate the undo plugin. Read the details in the Undo/Redo Functionality article.

The event is blockable. Returning false will cancel further processing.

The action parameter presents an array of command objects, each of which includes the following set of attributes:

type - (string) the type of a command: "add/remove/update"
entity - (string) the type of the object which was changed: "task" or "link"
value - (object) the changed task/link object
oldValue - (object) the task/link object before changes