How Can a Variadic Curried Sum Function in JavaScript Be Created Without Using the \' \' Babel Trick?

Variadic Curried Sum Without the Plus Babel Trick

Can JavaScript create a sum function that behaves like the following?

sum(1)(2) = 3
sum(1)(2)(3) = 6
sum(1)(2)(3)(4) = 10

It's mistakenly believed that this is impossible. However, it is feasible by leveraging the operator in combination with sum.

Solution:

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

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

  return v;
}

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

The key lies in the definition of valueOf and toString methods within the curried function. These methods dictate how the function behaves when coerced into a primitive value, such as a number. By returning n within these methods, we ensure that the curried function's internal state (the current sum) is preserved.

This technique enables the creation of a variadic curried sum function without relying on the babel trick.

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