SOURCE

function curry(fn) {
    return function cb (...args) {
        if(args.length >= fn.length) {
            return fn(...args)
        } else {
            return (...arg) => cb(...args, ...arg)
        }
    }
}


var demo = function (x, y, z) {
    return x + y + z
}

var curryFn = curry(demo)

console.log(curryFn(3)(2)(5))