How to use moment-duration-format in TypeScript?

You are using duration as a property instead of invoking it. Try:

let dd = moment.duration(400.99, 'hours').format('D:HH:mm');

This is actually not a TypeScript problem. It wouldn't work with JavaScript either. In JavaSctript you would get a runtime error while TypeScript doesn't let you do it at compile time (proving its worth).

I was using the workaround here, but it now looks like the ype def has been fixed. Getting an update of the type def So I can do the following...

import * as moment from 'moment';
import 'moment-duration-format';

let duration = moment.duration(decimalHours, 'hours') ;   
let options : moment.DurationFormatSettings   = {
  forceLength : false,
  precision : 0,
  template : formatString,
  trim : false
};
let result  = duration.format(formatString, 0, options);