# Nullish coalescing operator

The nullish coalescing operator (`??`) is a new operator introduced in ECMAScript 2020 (ES2020) that allows you to provide a default value for an expression if it is `null` or `undefined`. It is similar to the logical OR operator (`||`), but it only returns the default value if the expression is `null` or `undefined`, rather than any falsy value.

Here is an example of how to use the nullish coalescing operator:

```javascript
let x = null;
let y = undefined;
let z = 0;

console.log(x ?? 'default'); // 'default'
console.log(y ?? 'default'); // 'default'
console.log(z ?? 'default'); // 0
```

In this example, the nullish coalescing operator is used to provide default values for the variables `x` and `y`, which are `null` and `undefined`, respectively. The operator returns the default value of `'default'` for these variables, but it returns the value of `z` (`0`) as is, because `0` is not `null` or `undefined`.

The nullish coalescing operator can be useful in situations where you want to provide a default value for an expression, but you do not want to use a falsy value (such as `0`, `''`, or `false`) as the default. It can also be useful for distinguishing between `null` and `undefined`, which can be useful in certain cases.

For example, suppose you have a function that returns a user's name, or `null` if the user is not logged in. You could use the nullish coalescing operator to provide a default value for the user's name, like this

```javascript
function getUserName(user) {
  return user?.name ?? 'Guest';
}

console.log(getUserName({ name: 'Alice' })); // 'Alice'
console.log(getUserName(null)); // 'Guest'
console.log(getUserName({})); // 'Guest'
```

In this example, the nullish coalescing operator is used to provide a default value of `'Guest'` if the `user` object is `null` or `undefined`, or if the `user.name` property is `null` or `undefined`. If the `user.name` property is set to a non-nullish value, the operator returns that value instead.