编写一个函数来打印接受这个 wa 中的参数的总和： sum(2)(3) 并输出 5

Question

编写一个函数来打印以这种方式接受参数的总和： sum(2)(3) 并输出 5

Answer 1

What you're looking for is functional currying.

ES6

let sum = (first) => (second) => first + second;

ES5

function sum(first){ return function(second){  return first + second;}}

sum(2)(3);  //returns 5

Answer 2

Normally, you can achieve just like this

function sum(x) {
    return y => {
        return x + y;
    }
}

But it's kind of lack of extensibility. If you want to calculate sum(2)(3)(5) , this function just doesn't work.

You have to change it to

function sum(x) {
    return y => {
        return z => {
           return x + y + z;
        }
    }
}

Here is a common solution, combining recursion and a little trick.

function sum(x) {
    var result = x;
    function adder(y) {
        result += y;
        return adder;
    }
    adder.toString = function() {
        return result;
    };
    return adder;
}