@hello-pangea/dnd/src/state/auto-scroller/fluid-scroller/get-percentage.ts

Beautiful and accessible drag and drop for lists with React

import { warning } from '../../../dev-warning';

interface Args {
  startOfRange: number;
  endOfRange: number;
  current: number;
}

export default ({ startOfRange, endOfRange, current }: Args): number => {
  const range: number = endOfRange - startOfRange;

  if (range === 0) {
    warning(`
      Detected distance range of 0 in the fluid auto scroller
      This is unexpected and would cause a divide by 0 issue.
      Not allowing an auto scroll
    `);
    return 0;
  }

  const currentInRange: number = current - startOfRange;
  const percentage: number = currentInRange / range;
  return percentage;
};