isLeftClick :: Event

Event.isLeftClick(event) -> Boolean Determines whether a button-related mouse event was about the “left” (primary, actually) button.

Note: this is not an absolute left, but “left for default” (right-handed). On systems configured for left-handed users, where the primary button is the right one (from an absolute perspective), this function examines the proper button.

Prototype API 1.5.0 - prototypejs.org