indexCoordinatesConversions.js

// for use with pixel buffers, like the one you get from CanvasRenderingContext2D.getImageData(...).data
const getIndexFromCoordinates = (x, y, imageWidth) => y * (imageWidth * 4) + x * 4

const getCoordinatesFromindex = (index, imageWidth) => [
  (index / 4) % imageWidth,
  Math.floor((index / 4) / imageWidth)
];

// for use with normal arrays where one element represents a cell in a ROWSxCOLS grid 
const getIndexFromCoordinates = (x, y, width) => x + y * width;
const getCoordinatesFromIndex = (index, width) => [index % width, Math.floor(index / width)];