async-wait-until

A lightweight, zero-dependency library for waiting asynchronously until a specific condition is met. Works in any JavaScript environment that supports Promises, including older Node.js versions and browsers (with polyfills if necessary).

!npm version
!MIT License

✨ Features

- 🚀 Zero dependencies - Lightweight and fast
- 🔧 TypeScript support - Full TypeScript definitions included
- 🌐 Universal compatibility - Works in Node.js and browsers
- ⚡ Flexible configuration - Customizable timeouts and intervals
- 🎯 Promise-based - Clean async/await syntax
- 📦 Multiple formats - UMD, ESM, and additional format bundles
- 🛡️ Error handling - Built-in timeout error handling

📚 Table of Contents

- Installation
- How to Use
- API Reference
- TypeScript Usage
- Recipes
- Browser Compatibility
- Troubleshooting
- Development and Testing
- Links

📖 Detailed Documentation

For detailed documentation, visit https://devlato.github.io/async-wait-until/

---

🚀 Installation

Install using npm:

``sh
npm install async-wait-until
`

The library includes UMD and ESM bundles (plus additional formats), so you can use it in any environment.

`javascript
import { waitUntil } from 'async-wait-until';

// Example: Wait for an element to appear
await waitUntil(() => document.querySelector('#target') !== null);
`

---

🛠️ How to Use

$3

`javascript
import { waitUntil } from 'async-wait-until';

const waitForElement = async () => {
// Wait for an element with the ID "target" to appear
const element = await waitUntil(() => document.querySelector('#target'), { timeout: 5000 });
console.log('Element found:', element);
};

waitForElement();
`

$3

If the condition is not met within the timeout, a TimeoutError is thrown.

`javascript
import { waitUntil, TimeoutError } from 'async-wait-until';

const waitForElement = async () => {
try {
const element = await waitUntil(() => document.querySelector('#target'), { timeout: 5000 });
console.log('Element found:', element);
} catch (error) {
if (error instanceof TimeoutError) {
console.error('Timeout: Element not found');
} else {
console.error('Unexpected error:', error);
}
}
};

waitForElement();
`

---

📚 API Reference

$3

Waits for the predicate function to return a truthy value and resolves with that value.

Parameters:

| Name | Type | Required | Default | Description |
| --------------------------------- | ---------- | -------- | --------- | ------------------------------------------------------------------------------------ |
| predicate | Function | ✅ Yes | - | A function that returns a truthy value (or a Promise for one). |
| options.timeout | number | 🚫 No | 5000 ms | Maximum wait time before throwing TimeoutError. Use WAIT_FOREVER for no timeout. |
| options.intervalBetweenAttempts | number | 🚫 No | 50 ms | Interval between predicate evaluations. |

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| Name | Value | Description |
| --------------------------------------- | ----- | ---------------------------------------------- |
| WAIT_FOREVER | ∞ | Use for infinite timeout (no time limit). |
| DEFAULT_TIMEOUT_IN_MS | 5000| Default timeout duration in milliseconds. |
| DEFAULT_INTERVAL_BETWEEN_ATTEMPTS_IN_MS| 50 | Default interval between attempts in milliseconds. |

$3

- TimeoutError - Error thrown when timeout is reached before condition is met.

---

🔧 TypeScript Usage

This library is written in TypeScript and includes full type definitions. Here are some TypeScript-specific examples:

$3

`typescript
import { waitUntil, TimeoutError, WAIT_FOREVER } from 'async-wait-until';

// The return type is automatically inferred
const element = await waitUntil(() => document.querySelector('#target'));
// element is typed as Element | null

// With custom timeout and interval
const result = await waitUntil(
() => someAsyncCondition(),
{
timeout: 10000,
intervalBetweenAttempts: 100
}
);
`

$3

`typescript
// Async predicate example
const checkApiStatus = async (): Promise => {
const response = await fetch('/api/health');
return response.ok;
};

try {
await waitUntil(checkApiStatus, { timeout: 30000 });
console.log('API is ready!');
} catch (error) {
if (error instanceof TimeoutError) {
console.error('API failed to become ready within 30 seconds');
}
}
`

$3

`typescript
import { Options } from 'async-wait-until';

const customOptions: Options = {
timeout: 15000,
intervalBetweenAttempts: 200
};

await waitUntil(() => someCondition(), customOptions);
`

---

💡 Recipes

$3

Use WAIT_FOREVER to wait without a timeout:

`javascript
import { waitUntil, WAIT_FOREVER } from 'async-wait-until';

await waitUntil(() => someCondition, { timeout: WAIT_FOREVER });
`

$3

Change how often the predicate is evaluated:

`javascript
await waitUntil(() => someCondition, { intervalBetweenAttempts: 1000 }); // Check every 1 second
`

$3

`javascript
const waitForApi = async () => {
const response = await waitUntil(async () => {
try {
const res = await fetch('/api/status');
return res.ok ? res : null;
} catch {
return null; // Keep trying on network errors
}
}, { timeout: 30000, intervalBetweenAttempts: 1000 });

return response.json();
};
`

$3

`javascript
import fs from 'fs';
import { waitUntil } from 'async-wait-until';

// Wait for a file to be created
const filePath = './important-file.txt';
await waitUntil(() => fs.existsSync(filePath), { timeout: 10000 });

// Wait for file to have content
await waitUntil(() => {
if (fs.existsSync(filePath)) {
return fs.readFileSync(filePath, 'utf8').trim().length > 0;
}
return false;
});
`

$3

`javascript
const waitForDatabase = async (db) => {
await waitUntil(async () => {
try {
await db.ping();
return true;
} catch {
return false;
}
}, { timeout: 60000, intervalBetweenAttempts: 2000 });

console.log('Database is ready!');
};
`

$3

`javascript
// Wait for multiple conditions
const waitForComplexCondition = async () => {
return waitUntil(() => {
const user = getCurrentUser();
const permissions = getPermissions();
const apiReady = isApiReady();

// All conditions must be true
return user && permissions.length > 0 && apiReady;
});
};

// Wait for specific value ranges
const waitForTemperature = async () => {
return waitUntil(async () => {
const temp = await getSensorTemperature();
return temp >= 20 && temp <= 25 ? temp : null;
});
};
`

---

🌐 Browser Compatibility

This library works in any JavaScript environment that supports Promises:

Node.js: ✅ Version 0.14.0 and above
Modern Browsers: ✅ Chrome 32+, Firefox 29+, Safari 8+, Edge 12+
Legacy Browsers: ✅ With Promise polyfill (e.g., es6-promise)

$3

`html



`

$3

`html

`

---

🔍 Troubleshooting

$3

Q: My predicate never resolves, what's wrong?
A: Make sure your predicate function returns a truthy value when the condition is met. Common mistakes:
- Forgetting to return a value: () => { someCheck(); } ❌
- Correct: () => { return someCheck(); } ✅ or () => someCheck() ✅

Q: I'm getting unexpected timeout errors
A: Check that:
- Your timeout is long enough for the condition to be met
- Your predicate function doesn't throw unhandled errors
- Network requests in predicates have proper error handling

Q: The function seems to run forever
A: This happens when:
- Using WAIT_FOREVER without proper condition logic
- Predicate always returns falsy values
- Add logging to debug: () => { const result = myCheck(); console.log(result); return result; }

Q: TypeScript compilation errors
A: Ensure you're importing types correctly:
`typescript
import { waitUntil, Options, TimeoutError } from 'async-wait-until';
`

$3

- Use reasonable intervals (50-1000ms) to balance responsiveness and CPU usage
- For expensive operations, increase the interval: { intervalBetweenAttempts: 1000 }
- Implement proper error handling in async predicates to avoid unnecessary retries
- Consider using WAIT_FOREVER with external cancellation for long-running waits

---

🧪 Development and Testing

Contributions are welcome! To contribute:

1. Fork and clone the repository.
2. Install dependencies: npm install.
3. Use the following commands:

- Run Tests: npm test
- Lint Code: npm run lint
- Format Code: npm run format
- Build Library: npm run build
- Generate Docs: npm run docs`

---

📝 Links

- License
- Detailed Documentation
- Changelog - Track version updates and changes
- Contributing Guidelines - How to contribute to the project
- Code of Conduct - Community standards and expectations