Script to use on http://www.theguardian.com/us-news/ng-interactive/2015/jun/01/the-counted-police-killings-us-database# to find out the longest time between killings.

us-police-killings.js

// The Counted uses lazy loading so make sure to scroll slowly down
// the page to the bottom before trying to run this or your count will
// be off.
let elements = Array.from(document.querySelectorAll('.record-inner .date'));
let dates = elements.map(e => new Date(e.innerHTML)).reverse();

let initialState = {
  previousDate: dates.shift(),
  maxDifference: 0,
  count: 0,
  dateRanges: [],
};

// Find out the max time between police shootings and keep track of ties.
let max = dates.reduce((state, currentDate) => {
  let currentDifference = currentDate - state.previousDate;
  if (currentDifference > state.maxDifference) {
    state.count = 1;
    state.maxDifference = currentDifference;
    state.dateRanges = [ [state.previousDate, currentDate] ];
  } else if (currentDifference == state.maxDifference) {
    state.count += 1;
    state.dateRanges.push([state.previousDate, currentDate]);
  }
  state.previousDate = currentDate;
  return state;
}, initialState);

console.log(max);