dateDiff.js

const dateDiff = (d1, d2, type = "days") => {

    const date1 = d1 instanceof Date ? d1 : new Date(`${d1.slice(6)}, ${d1.slice(3, 5)}, ${d1.slice(0, 2)}`)

    const date2 = d2 instanceof Date ? d2 : new Date(`${d2.slice(6)}, ${d2.slice(3, 5)}, ${d2.slice(0, 2)}`)

    return {

        days: () => {

            return Math.floor((date2.getTime() - date1.getTime()) / (24 * 3600 * 1000))
        },

        weeks: () => {

            return Math.floor((date2.getTime() - date1.getTime()) / (24 * 3600 * 1000 * 7))

        },

        months: () => {

            return Math.floor((date2.getMonth() + (date2.getFullYear() * 12)) - (date1.getMonth() + (date1.getFullYear() * 12)))

        },

        years: () => {

            return date2.getFullYear() - date1.getFullYear()
        }

    }[type]()

}

console.log(dateDiff("05/05/2011", new Date(), "years"))