SOURCE

Function.prototype.getValue = function () {
    let num = this.arr.reduce((x, y) => x + y)
    this.arr = []
    return num
}

const foo = function (...args) {
    if (!Array.isArray(foo.arr)) {
        foo.arr = []
    }
    foo.arr.push(...args)
    return foo
}

var f3 = foo(1)(2)(3)(4); console.log(f3.getValue()); // 10