sometimesalready

let R = require('ramda')

var prepend = R.when(
    R.propSatisfies(R.lt(R.__, 2), 'length'),
    R.pipe(R.prepend(0), R.join(''))
);

let normalize = R.pipe(R.toLower, R.split(':'), R.map(prepend), R.join(':'));

normalize('4:46:65:F2:2b:7'); //=> 04:46:65:f2:2b:07