How Can a Curried Sum Function in JavaScript Handle Multiple Arguments?

Currying a Variadic Sum Function: Exploring Its Inner Workings

In JavaScript, creating a sum function that accepts multiple arguments and works in a curried manner may seem like an insurmountable task. However, it is indeed possible with the technique of currying.

Currying involves converting a function that takes multiple arguments into a series of functions, each taking a single argument. This enables us to create a sum function that can be applied sequentially to add multiple numbers.

The secret lies in the way we define the function:

function sum(n) {
  var v = function(x) {
    return sum(n + x);
  };

Here, sum(n) returns a function v that takes one argument x and returns the result of calling sum with n x. This allows us to chain multiple calls to sum, each adding the next number to the previous result.

To handle the final result, we define the valueOf and toString methods of the function:

  v.valueOf = v.toString = function() {
    return n;
  };

This ensures that when we invoke v as a value, it returns the accumulated sum n.

Finally, we use the unary plus operator ( ) to convert the result of the curried function into a primitive number.

console.log(+sum(1)(2)(3)(4));

This outputs the expected result: 10.

So, while it may seem counterintuitive at first, creating a variadic curried sum function in JavaScript is possible using the principles of currying and clever manipulation of function properties.

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