Blog "Leibniz equality in TypeScript", aside `zoom`

aside_zoom.ts

function zoom(dayStart: number, dayEnd: number, zoomFactor: number): [number, number] {
  // What is the middle of the time range?
  // When zooming in or out, the middle of the time range should stay the middle.
  const dayMiddle = (dayEnd + dayStart) / 2
 
  // Determine what the new time range should be using the `zoomFactor`.
  const oldTimeRange = dayEnd - dayStart
  const newTimeRange = oldTimeRange * zoomFactor
 
  // Calculate the new boundaries of the time range:
  const newDayStart = dayMiddle - newTimeRange / 2
  const newDayEnd = dayMiddle + newTimeRange / 2
  
  return [newDayStart, newDayEnd]
}