SOURCE

/**
 * Mying
 */
function add() {
    let args = [...arguments]
    let fun = function () {
        // console.log(args,arguments)
        args.push(...arguments)
        return fun
    }
    fun.toString = function () {
        return args.reduce(function (a, b) {
            return a + b
        })
    }
    return fun
}
sum = add(1,2)(3)(4)(5,6)

console.log(sum)