Hi:

Was wondering if someone could explain why a comma followed by a zero is required in the ‘reduce’ function ((((( return args.reduce((a, b) => a + b, 0); )))))?. Thanks.

**Your code so far**

```
const sum = (function() {
"use strict";
return function sum(...args) {
return args.reduce((a, b) => a + b, 0);
};
})();
console.log(sum(1, 2, 3)); // 6
```

**Your browser information:**

User Agent is: `Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/68.0.3440.106 Safari/537.36`

.

**Link to the challenge:**

https://learn.freecodecamp.org/javascript-algorithms-and-data-structures/es6/use-the-rest-operator-with-function-parameters