maximumProfit.js

// calcuale the greatest profit
function evaluate() {
  // store greatest profit
  let evaluation = -1;

  // calculate position
  return function (min, max) {
    const profit = max - min;

    evaluation = evaluation < profit ? profit : evaluation;
    return evaluation;
  };
}

// Find maximum profit
function maximumProfit(arr) {
  // declare min node, evaution function and result
  let min = arr[0],
    profit = -1;
  const evaluation = evaluate();

  for (let i = 1; i < arr.length; i++) {
    
    // when the current position is greater than min value
    if (arr[i] > min) {
      // calculate profit
      profit = evaluation(min, arr[i]);
    }

    // only set min if less then previous position
    if (arr[i] < min) {
      min =  arr[i];
    }
  }

  return profit;
}

Code from a recent challenge.