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JavaScript jQuery Basics (2014) Creating a Simple Drawing Application Perform: Part 5

Posted by Osama Awan
Osama Awan
Courses Plus Student 8,676 Points

What does `lastEvent = e` means?

I didn't get why Andrew reassign the LastEvent to the current e object in mouse move function .

$canvas.mousedown(function(e) {
  lastEvent = e;
}).mousemove(function(e) {
  context.beginPath();
  context.moveTo(lastEvent.offsetX, lastEvent.offsetY);
  context.lineTo(e.offsetX, e.offsetY);

  context.stroke();
  lastEvent = e;

});`

1 Answer

Steven Parker
Steven Parker
231,275 Points
Steven Parker
Steven Parker
231,275 Points

:point_right: The event object (e) is saved to use the location for drawing.

The location where the last event occurred is passed to context.moveTo (about the center of your code snippet) to establish the beginning of the line segment being drawn. So for any mouse click or move, the last thing done by the handler is to save the current location by assigning the event object to lastEvent.

The location coordinates could have been saved individually, but it is convenient to save the entire event object.