# decorator-synchronized

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> Function decorator which ensures that calls do not run simultaneously.

Requires _WeakMap_, it your system does not have it, use a [polyfill](https://github.com/medikoo/es6-weak-map).

## Install

Installation of the [npm package](https://npmjs.org/package/decorator-synchronized):

```
> npm install --save decorator-synchronized
```

## Usage

```js
import { synchronized } from "decorator-synchronized";

let i = 0;

const fn = synchronized(() => {
  console.log(i);
  return Promise.resolve().then(() => {
    i++;
  });
});

Promise.all([fn(), fn()]);
// => Prints 0 then 1

// Create a dedicated synchronizer which will be shared amongst
// multiple functions.
//
// Useful when functions work on the same resource.
const counterSynchronized = synchronized();

const increment = counterSynchronized(async () => {
  const i = 1 + (await db.getCounter());
  await db.setCounter(i);
  return i;
});

const decrement = counterSynchronized(async () => {
  const i = -1 + (await db.getCounter());
  await db.setCounter(i);
  return i;
});

increment().then(console.log); // prints 1
decrement().then(console.log); // prints 0
```

### `withKey`

```js
import { synchronized } from "decorator-synchronized";

const updateUser = synchronized.withKey()(async (userId, props) => {
  const user = await db.getUser(userId);
  await db.setUser(userId, { ...user, ...props });
});

// will correctly update the user without race conditions
updaterUser("wq1567e", { foo: 3.14 });
updaterUser("wq1567e", { bar: 42 });

// different users are still updated in parallel
updateUser("ct356tv", { baz: 2.72 });
```

The key is deduced from the first argument, if you need something
else, just provide a key function:

```js
const fn = synchronized.withKey((_, secondArg) => secondArg)(
  (firstArg, secondArg) => {
    // TODO
  }
);
```

## Development

```
# Install dependencies
> yarn

# Run the tests
> yarn test

# Continuously compile
> yarn dev

# Continuously run the tests
> yarn dev-test

# Build for production
> yarn build
```

## Contributions

Contributions are _very_ welcomed, either on the documentation or on
the code.

You may:

- report any [issue](https://github.com/JsCommunity/decorator-synchronized/issues)
  you've encountered;
- fork and create a pull request.

## License

ISC © [Pierre Donias](https://github.com/pdonias)