Espruino on your (Xiaomi) humidity sensor

Is the LCD attached via SPI or something like that? I'd say it almost certainly is easier to send all data all the time especially given the overhead of running JS.

If there are 32 or less segments I'd just try and use a Uint32Array where each element is a mask of the segments that need to be turned on for a word.

var segChars="0123456789abcdef";
var segMask = new Uint32Array([.......]);

The you just use 'or' to add all the segments you need together, and send the result as bytes.