The MouseEvent() constructor creates a new MouseEvent.
The KeyboardEvent.metaKey read-only property returning a Boolean that indicates if the Meta key was pressed (true) or not (false) when the event occurred.  Some operating systems may intercept the key so it is never detected.
The MouseEvent.altKey read-only property is a Boolean indicates if the alt key was pressed (true) or not (false) when the event occurred.
The MouseEvent.button read-only property indicates which button was pressed on the mouse to trigger the event.
The MouseEvent.ctrlKey read-only property returns a Boolean that indicates if the control key was pressed (true) or not (false) when the event occured.
The MouseEvent.getModifierState() method returns the current state of the specified modifier key: true if the modifier is active (i.e., the modifier key is pressed or locked), otherwise, false.
The MouseEvent.region read-only property returns the id of the canvas hit region affected by the event. If no hit region is affected, null is returned.
The MouseEvent.relatedTarget read-only property is the secondary target for the event, if there is one. That is:
The MouseEvent.screenY read-only property provides the vertical coordinate of the mouse pointer in global (screen) coordinates.
The MouseEvent.shiftKey read-only property indicates if the shift key was pressed (true) or not (false) when the event occurred.
The MouseEvent.clientX read-only property provides the horizontal coordinate within the application's client area at which the event occurred (as opposed to the coordinates within the page). For example, clicking in the top-left corner of the client area will always result in a mouse event with a clientX value of 0, regardless of whether the page is scrolled horizontally.
The MouseEvent.clientY read-only property returns the vertical coordinate within the application's client area at which the event occurred (as opposed to the coordinates within the page). For example, clicking in the top-left corner of the client area will always result in a mouse event with a clientY value of 0, regardless of whether the page is scrolled vertically.
The MouseEvent.movementY read-only property provides the shift in the Y coordinate of the mouse pointer between that event and the previous mousemove event. In other words, the value of that property is computed that way : currentEvent.movementY = currentEvent.screenY - previousEvent.screenY.
The MouseEvent.screenX read-only property provides the horizontal coordinate of the mouse pointer in global (screen) coordinates.