Using the moment.js time duration shorthand to get number of seconds from a string. Say the inputString is '3y' or '5M' or '2d', this would give you the respective time from now in seconds.

gistfile1.js

// I don't love this but its a quick/dirty create of cache duration using moment's nice date add format
// parse cache duration as [integer][unit] via http://momentjs.com/docs/#/manipulating/add/ shorthand
var durations = /^([\d]+)([\w]+)/.exec(inputString);
var invalidateSeconds = moment(0).add(durations[2],durations[1]).unix();