我怎样才能让这个 javascript 函数调用自己？

Question

As of right now my sum function looks like the code below. It works and returns the sum of the consecutive calls. But how can I make this work without the empty parenthesis at the end? Like so theSum(5)(4)(3) which returns 12.

function theSum(x) {
    var total = x;

    function rec(y) {
        if (y === undefined) return total;
        total += y;
        return rec;
    };

    return rec;
}

console.log(theSum(5)(4)(3)()); // 12

Answer 1

Here is a suggestion utilizing a toString method:

function theSum(x) {
    var total = x;

    function rec(y) {
        total += y;
        return rec;
    };

    rec.toString = function() { return total; }

    return rec;
}

alert(theSum(5)(4)(3));

console.log(parseInt(theSum(5)(4)(3)));

Note however that you need to convert the returned reference to a string in some way so that you see the result.

Answer 2

This is not possible. A function cannot return a function and an integer. You can make theSum(5, 4, 3) = 12 or theSum([5, 4, 3]) = 12 .

Answer 3

Closures and JavaScript duck typing to the rescue:

function NumSumFun(initial){
    function NumSumNext(num) {
          initial+= num;
      return NumSumNext;
    }
    NumSumNext.valueOf = function () { return initial; }
    return NumSumNext;
}

var x = NumSumFun(10)(29); // ==> function 39
x + 1; // ==> 40

So whats happening. It returns a function but the function has a valueOf property that has access to the accumulated value so the function acts as a number when used as a number.