sinProject-Inc/sinpro-dev

---
title: Concurrency
description: This is a guide to producing readable, reusable, and refactorable software for TypeScript.
---

## Use fs.promises

```ts::Bad
import fs from 'fs'

const file = fs.readFileSync(...)
```

```ts::Good
import fs from 'fs'

const file = await fs.promises.readFile(...)
```

## Use Promises, not callbacks

```ts::Bad
public async get_hostname(): Promise<string> {
    const hostname: string[] = await new Promise<string[]>((resolve) => {
        dns.reverse(this._client_address, (e, hostnames) => {
            if (e) {
                console.warn('Reverse DNS lookup failed.', e)
                resolve([])
            } else {
                resolve(hostnames[0])
            }
        })
    })

    return hostname
}
```

```ts::Good
public async get_hostname(): Promise<string> {
    const reverse_dns = util.promisify(dns.reverse)

    try {
        const hostnames = await reverse_dns(this._client_address)
        return hostnames[0]
    } catch (e) {
        console.warn('Reverse DNS lookup failed.', e)
        return ''
    }
}
```