While doing some JavaScript challenges, I faced with the code add(1)(2), a function being called with several parenthesis. The challenge is to make a chain of add function.
add(1)(2)(3); // -> 6
add(1)(2)(3)(4); // -> 10
add(1)(2)(3)(4)(5); // -> 15
Also, we should be able to store the returned values and reuse them.
var addTwo = add(2);
addTwo; // -> 2
addTwo + 5; // -> 7
addTwo(3); // -> 5
addTwo(3)(5); // -> 10
Thanks in advance.
function sum(firstArg, opt_argsStack) {
const argsStack = (opt_argsStack || []).concat([firstArg]);
const nextSum = nextArg => sum(nextArg, argsStack);
nextSum.valueOf = () => argsStack.reduce((a, b) => a + b);
return nextSum;
}
console.log(+sum(1));
console.log(+sum(1)(2));
console.log(+sum(1)(2)(3));
console.log(+sum(1)(2)(3)(4));
Here, we pass the stack of all accumulated arguments down to recursive call. And in valueOf call, stack is transformed to a number via reduce just in time. This gives us more flexibility, imo, if we wanted to change chained sum to chained multiplication or whatever else — we just plug in different reduce function.
