# 3 Ways to set default values

### 1. Variables

The [nullish coalescing operator (`??`)](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Nullish_coalescing_operator) is a logical operator that returns its right-hand side operand when its left-hand side operand is `null` or `undefined` and otherwise returns its left-hand side operand. We can use this to set default values, for example when we receive a list that has not been set to an array yet:

```
const bookList = receivedBooks ?? [];
```

### 2. Parameters

We could use the *null coalescing operator* to set defaults for variables in functions but there is a better way, [default parameters](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Default_parameters):

```
function calculateArea(width, height = 100) {
    return width * height;
}

const area = calculateArea(50);
console.log(area); // 5000

```

### 3. Objects

We can also give default value once we destructure object properties. ES6 destructuring default values only kick in if the value is `undefined`.

```
const rectangle = { height: 400 };
const { height = 750, width = 500 } = rectangle;
console.log(height); // 400 - comes from rectangle object
console.log(width);  // 500 - fallback to default

```

## Links
- [nullish coalescing operator (`??`)](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Nullish_coalescing_operator)
- [default parameters](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Default_parameters)