Google Step one

widest-interval.js

const data = [50, 60, 40, 80, 30, 56, 63, 42, 65, 23];

const findWidestInterval = (data) => {
  if (Array.isArray(data) && !!data.length) {
    const maxLostInterval = 0;

    for (let i = 0; i < data.length - 1; i += 1) {
      for (let j = i; j < data.length - 1; j += 1) {
        const startPrice = data[i];
        const endPrice = data[j];
        const lost = startPrice-endPrice;
        const interval = j-i;

        if(lost < 0 && interval>maxLostInterval) maxLostInterval = interval
      
      }
    }

    return maxLostInterval;
  }
  return 0;
};