Format hours, minutes and seconds with moment.js

I am not sure if momentjs can read that as date since there is no identifier. I would suggest changing the value for example you have 171054, get each 2 digits since you sure that this is represent as hh:mm:ss then add identifier between then like ":" or "-" then try us momentjs formatting again.

You are confusing format option with parsing option. Since your input string is not in ISO 8601 format, you have to specify format when parsing.

Here a working example for your use case:

var mom = moment('171054', 'HHmmss');
console.log(mom.format());
console.log(mom.format('HH:mm:ss'));

<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.15.1/moment.min.js"></script>