Mathematical boundaries (audio meter)
vumeter % 50 &lt; vumeter doesn't make much sense to me. For non-negative numbers, this is equivalent to vumeter &gt; 50, so you can just use that instead. For negative numbers, this will always return false, although it seems like this would be an illegal argument to your function.

@mleyfman provided a great solution. In practice, the code provided achieves something called clamping, where you restrict a value to a specified range. You can roll your own clamp function like so:

clamp = (value, min, max) -&gt; Math.min(Math.max(min, value), max)

levels = (vumeter) -&gt;
  'green'  : clamp(vumeter,  0,  50)
  'yellow' : clamp(vumeter, 50,  85) - 50
  'red'    : clamp(vumeter, 85, 100) - 85
  // or, if you find it more meaningful to provide maxima as parameters rather than ranges:
  'green': clamp(vumeter, 0, 50)
  'yellow': clamp(vumeter - 50, 0, 35)
  'red': clamp(vumeter - 85, 0, 15)