count-to-6/lib/exercises/default_arguments_part_1/problem.md

An intro to some ES6 features via a set of self-guided workshops.

In ES6, functions can take default arguments:

```js
function sayHello(greeting = "Hello", name = "CampJS") {
    console.log(`${greeting} ${name}!`);
}
```

When you call the function without arguments in those positions, the default ones are applied instead:

```js
sayHello();            // "Hello CampJS!"
sayHello("Hi there");  // "Hi there CampJS!"
```

You can also use `undefined` in any argument position to trigger the default:

```js
sayHello(undefined, undefined); // "Hello CampJS!"
sayHello("Hiya", undefined);    // "Hiya CampJS!"
sayHello(undefined, "JSConf");  // "Hello JSConf!"
```

Note that other values will *not* trigger the defaulting, even falsy values like `null`, `false`, `""`, or `0`:

```js
sayHello(null, 0); // "null 0!"
```

## Challenge

As in the **rest** parameters exercise, your goal is to write a Node module whose default export is a function. This time it will take two arguments: a lower bound and an upper bound. Your function should return the midpoint between those two bounds.

However, your function should have sensible defaults. The lower bound should default to `0`, and the upper bound should default to `1`.

As before, you don't need to print anything to the console. Your solution should look something like:

```js
module.exports = function midpoint(/* what goes here */) {
    // what goes here?
};
```

We'll test your module by passing it a few different sets of arguments: sometimes none, sometimes one, sometimes two. Sometimes we'll pass in an explicit `undefined`, and you should be sure to treat that as the default.