Arguments Optional

From: https://www.freecodecamp.org/learn/javascript-algorithms-and-data-structures/intermediate-algorithm-scripting/arguments-optional

Intermediate Algorithm Scripting: Arguments Optional


Create a function that sums two arguments together. If only one argument is provided, then return a function that expects one argument and returns the sum.

For example, addTogether(2, 3) should return 5, and addTogether(2) should return a function.

Calling this returned function with a single argument will then return the sum:

var sumTwoAnd = addTogether(2);

sumTwoAnd(3) returns 5.

If either argument isn't a valid number, return undefined.


addTogether(2, 3) should return 5.

addTogether(23, 30) should return 53.

addTogether(5)(7) should return 12.

addTogether("http://bit.ly/IqT6zt") should return undefined.

addTogether(2, "3") should return undefined.

addTogether(2)([3]) should return undefined.

function addTogether(a, b) {
    if (typeof a === 'number') {
        if (typeof b === 'number') {
          return a + b;
        } else if (b === undefined) {
          return toAdd => addTogether(a, toAdd);
        } 
    }
}

[
    addTogether(2, 3),
    addTogether(23, 30),
    addTogether(5)(7),
    addTogether(2, "3"),
    addTogether(2)([3])
].forEach(result => console.log(result));

Output:

5
53
12
undefined
undefined