---
id: 598e8944f009e646fc236146
title: Understanding Undefined Value returned from a Function
challengeType: 1
forumTopicId: 301177
dashedName: understanding-undefined-value-returned-from-a-function
---

# --description--

A function can include the `return` statement but it does not have to. In the case that the function doesn't have a `return` statement, when you call it, the function processes the inner code but the returned value is `undefined`.

**Example**

```js
let sum = 0;

function addSum(num) {
  sum = sum + num;
}

addSum(3);
```

`addSum` is a function without a `return` statement. The function will change the global `sum` variable but the returned value of the function is `undefined`.

# --instructions--

Create a function `addFive` without any arguments. This function adds 5 to the `sum` variable, but its returned value is `undefined`.

# --hints--

`addFive` should be a function.

```js
assert(typeof addFive === 'function');
```

Once both functions have run, the `sum` should be equal to `8`.

```js
assert(sum === 8);
```

Returned value from `addFive` should be `undefined`.

```js
assert(addFive() === undefined);
```

Inside the `addFive` function, you should add `5` to the `sum` variable.

```js
assert(
  __helpers.removeWhiteSpace(addFive.toString()).match(/sum=sum\+5|sum\+=5/)
);
```

# --seed--

## --seed-contents--

```js
// Setup
let sum = 0;

function addThree() {
  sum = sum + 3;
}

// Only change code below this line


// Only change code above this line

addThree();
addFive();
```

# --solutions--

```js
let sum = 0;

function addThree() {
  sum = sum + 3;
}

function addFive() {
  sum = sum + 5;
}

addThree();
addFive();
```