Check if a number is inside a given range with JavaScript

Given a number and a range, you can check if the number falls within the specified range. This can be useful when you need to validate user input or filter a list of numbers.

As the simplest solutions are often the best, we need only use arithmetic comparison to check if the number is in the specified range. If the second argument, end, is not specified, the range is considered to be from 0 to start. If, however, the start value is greater than the end value, we can swap them to ensure that the range is valid.

const inRange = (n, start, end = null) => {
  if (end && start > end) [end, start] = [start, end];
  return end == null ? n >= 0 && n < start : n >= start && n < end;
};

inRange(3, 2, 5); // true
inRange(3, 4); // true
inRange(2, 3, 5); // false
inRange(3, 2); // false