Variable length currying in JavaScript

possibilities.js

// This cannot be true with the following statement.
addSubtract(1)(2)(3) === 0;

// This cannot be true with the preceding statement.
addSubtract(1)(2)(3)(4)(5)(6) === 5;

// This can be true:
addSubtract(1)(2)(3) + addSubtract(1)(2)(3)(4)(5)(6) === 5;

// These can be true too:
+addSubtract(1)(2)(3) === 0;
+addSubtract(1)(2)(3)(4)(5)(6) === 5;