How can I get this javascript function to call itself?

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

You could use a toString method. I can't imagine where this kind of chaining will be useful :? — php_nub_qq
– php_nub_qq, Commented Mar 28, 2016 at 22:49
Its not really clear what youre trying to achieve, besides the obvious. But why the chain, I dont get it. My original answer, solved this issue, in a different way, but you didnt find it useful. So be more concise as to why you want to do it this way. as @php_nub_qq says. "I cant imagine where this could be useful" So let us know, wh its useful to you. And why is theSum(5)(4)(3) more important to achieve to you, than theSum(5)(4)(3)() or theSum([5,4,3])? Or is this a homework question, and you're not even sure youirself — Kylie
– Kylie, Commented Mar 28, 2016 at 23:04

php_nub_qq · Accepted Answer · 2016-03-28 23:12:42Z

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.

answered Mar 28, 2016 at 23:12

php_nub_qq

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2 Comments

stack_pooper Over a year ago

This returns { [Function: rec] toString: [Function] } in NodeJS

php_nub_qq Over a year ago

@stack_pooper yes, that is what it returns, converting it to a string is where the magic happens. Nice name btw.

user6101582 · Accepted Answer · 2016-03-28 22:55:12Z

0

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.

answered Mar 28, 2016 at 22:55

user6101582

Comments

Sylwester · Accepted Answer · 2016-03-29 00:36:00Z

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.

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