Util.js

import d3 from 'd3';

/**
 * Like d3.bisect but chooses the closest element, not always the left or right
 * That is, finds the element in the array closest to the value through the use of accessor
 */
export function findClosest(array, value, accessor) {
  if (!array || !array.length) {
    return null;
  }

  const bisect = d3.bisector(accessor).right;
  const pointIndex = bisect(array, value);
  const left = array[pointIndex - 1], right = array[pointIndex];

  let element;

  // take the closer element
  if (left && right) {
    element = Math.abs(value - accessor(left)) < Math.abs(value - accessor(right)) ? left : right;
  } else if (left) {
    element = left;
  } else {
    element = right;
  }

  return element;
}