SOURCE

//场景：写一个sum函数计算三个数的和
a = 2
b = 3
c = 4
function sum1(a, b, c) {
    return a + b + c
}

function sum(a) {
    return function (b) {
        return function (c) {
            return a + b + c
        }
    }
}

console.log(sum1(a, b , c))
console.log(sum(a)(b)(c))