Reading Apple Pencil Pressure in the Browser — PointerEvent, getCoalescedEvents(), and the e.pressure Trap

Building a sketch pad in a browser sounds like a one-evening job. Then someone tries it with an Apple Pencil and the pressure data is gone , because the code listens for mousemove . Or with a mouse and the line is half as thick as it should be, because it reads e.pressure blindly and a mouse reports 0.5 . Or with a fast hand on an iPad and the line is jagged , because the browser only emits one pointermove per 60 Hz frame and the Apple Pencil samples at 240 Hz. This 300-line page solves all thre