# call-to-promise
[](https://www.npmjs.com/package/call-to-promise)
[](https://github.com/dominikj111/prutill/blob/main/package.json)
[](https://coveralls.io/r/boennemann/badges)
[](https://github.com/dwyl/goodparts 'JavaScript The Good Parts')
A lightweight, production-ready, universal library for transforming callback-style functions into Promise-based ones.
Works seamlessly across Node.js, Deno, and browsers.
> **📌 Maintenance Status**: This library is in maintenance mode. It is well-written, thoroughly tested, and production-ready.
> Modern JavaScript provides built-in solutions for most promise-related use cases. However,
> this library remains a reliable choice with zero dependencies (thus zero vulnerabilities)
> if you need its specific ID-based promise storage feature. While no new features are being developed,
> bug reports are monitored and fixes are provided when needed.
## 🚀 Who's Using This?
If you use this project, I'd love to know! Feel free to reach out or star this repo.
## ✨ Features
- 🌐 **Universal Compatibility**: Works in Node.js, Deno, and browsers
- 🔒 **Type Safety**: Full TypeScript support with type definitions
- 🎯 **Zero Dependencies**: Lightweight and self-contained
- 🔄 **Promise Chaining**: Full support for Promise chaining and async/await
- 📦 **Multiple Module Formats**: UMD and ES Module bundles available
- ✅ **Production Ready**: Battle-tested and fully covered with tests
## 🛠️ Installation
### NPM/Yarn
```bash
npm install call-to-promise
# or
yarn add call-to-promise
```
### Browser
```html
```
### Deno
```javascript
import * as c2p from 'path/to/dist/module.min.mjs';
```
## Usage
### Basic Example
```javascript
const c2p = require('call-to-promise'); // or import for ES modules
function add(a, b, callback) {
callback(a + b);
}
// Convert callback to promise
add(3, 4, c2p.successfn('add-result'));
c2p.when('add-result').then(console.log); // -> 7
```
### Multiple Arguments
```javascript
function calculate(a, b, callback) {
callback(a + b, a * b, a - b);
}
calculate(3, 4, c2p.successfn('calc'));
c2p.when('calc').then(console.log); // -> { '0': 7, '1': 12, '2': -1 }
```
### File System Example (Node.js)
```javascript
const c2p = require('call-to-promise');
const fs = require('fs');
fs.readFile('/etc/hosts', 'utf8', c2p.successfn('read-file'));
c2p.when('read-file').then(([err, data]) => {
if (err) throw err;
console.log(data);
});
```
### Multiple Promises
```javascript
c2p
.when(['promise1', 'promise2', 'promise3'])
.then((results) => console.log(results));
```
### Local vs Global Instance
```javascript
// Global instance (shared across modules)
const c2p = require('call-to-promise');
// Local instance (isolated)
const localC2p = require('call-to-promise').build();
```
## Modern Alternatives
While this library remains reliable, here are modern approaches to handle similar scenarios:
### 1. Using Node.js util.promisify
```javascript
const { promisify } = require('util');
const fs = require('fs');
// Convert callback-based function to promise-based
const readFileAsync = promisify(fs.readFile);
// Use it
async function readConfig() {
try {
const data = await readFileAsync('/etc/hosts', 'utf8');
console.log(data);
} catch (err) {
console.error(err);
}
}
```
### 2. Using Promise Constructor
```javascript
function promisifyFunction(fn) {
return (...args) => {
return new Promise((resolve, reject) => {
fn(...args, (err, result) => {
if (err) reject(err);
else resolve(result);
});
});
};
}
// Example usage
const readFilePromise = promisifyFunction(fs.readFile);
readFilePromise('/etc/hosts', 'utf8').then(console.log).catch(console.error);
```
### 3. Modern APIs (Already Promise-based)
```javascript
// Modern Web APIs are already promise-based
fetch('https://api.example.com/data')
.then((response) => response.json())
.then((data) => console.log(data))
.catch((error) => console.error(error));
// Modern Node.js APIs often provide promise versions
const { readFile } = require('fs/promises');
readFile('/etc/hosts', 'utf8').then(console.log).catch(console.error);
```
### When to Use This Library?
- You need to store and manage promises by ID
- You're working with legacy callback-based code and need a consistent way to handle promise creation and storage
- You want a zero-dependency solution that works across all JavaScript environments
## 📚 API Reference
### Main Functions
- `successfn(id: string)`: Creates a success callback for the given ID
- `failfn(id: string)`: Creates a failure callback for the given ID
- `when(id: string | string[])`: Returns a Promise for the given ID(s)
- `id(id: string)`: Returns the deferred object for direct manipulation
- `build()`: Creates a new local instance
### Deferred Object Methods
- `isPending()`: Checks if the promise is pending
- `isSucceed()`: Checks if the promise is fulfilled
- `isFailed()`: Checks if the promise is rejected
- `resolve(value)`: Resolves the promise
- `reject(error)`: Rejects the promise
## 📄 License
BSD-3-Clause © dominikj111
This library is licensed under the BSD 3-Clause License.
---
Made with ❤️ because I love coding