code: function findClosestValue (values, lookupVal) {
    let diff = 1;
    let id = 0;
  
    values.forEach((value, index) => {
      const actualDiff = Math.abs(value - lookupVal);
      if (actualDiff < diff) {
        id = index;
        diff = actualDiff;
      }
    });
  
    return id;
  }
docs: Returns id of value in this.values, which is closest to `lookupVal`