var dateFns = require("date-fns")
var totalDuration = dateFns.intervalToDuration({
start: new Date(1929, 0, 15, 12, 0, 0),
end: new Date(1968, 3, 4, 19, 5, 0)
})
dateFns.formatDuration(totalDuration, { format: ['years', 'months'], delimiter: ', ' })
Created from: https://npm.runkit.com/date-fns