Question

I would like to know how the events are generated in jquery-ui Sortable Widget?

For example. let’s take the event beforeStop.
My questions are:

1. why does it use this._trigger("stop", event, this._uiHash()); instead of this.trigger("stop", event, this._uiHash());?

2. what does _trigger function?

Answer 1

_trigger() is a method inherited by all jQuery UI widgets. It calls jQuery’s own trigger() under the hood, but adds the following functionality:

• The event will be always be triggered on the element the widget augments (the target property of the event object is updated accordingly).

• The event that is triggered has the widget prefix prepended to its name (for instance, calling _trigger("stop") on a sortable widget will actually trigger the sortstop event).

• The function returns false if one of the registered handlers either returns false or calls preventDefault() on the event.

You can find the full implementation of _trigger() from lines 476 to 503 in the source code here.