devlato
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).
✨ 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:
npm install async-wait-untilThe library includes UMD and ESM bundles (plus additional formats), so you can use it in any environment.
import { waitUntil } from 'async-wait-until';
// Example: Wait for an element to appear
await waitUntil(() => document.querySelector('#target') !== null);🛠️ How to Use
Basic Example: Wait for a DOM Element
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();Handling Timeouts
If the condition is not met within the timeout, a TimeoutError is thrown.
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
waitUntil(predicate, options)
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. |
Exported Constants
| 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. |
Exported Classes
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:
Basic TypeScript Usage
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
}
);Using with Async Predicates
// Async predicate example
const checkApiStatus = async (): Promise<boolean> => {
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');
}
}Type-Safe Options
import { Options } from 'async-wait-until';
const customOptions: Options = {
timeout: 15000,
intervalBetweenAttempts: 200
};
await waitUntil(() => someCondition(), customOptions);💡 Recipes
Wait Indefinitely
Use WAIT_FOREVER to wait without a timeout:
import { waitUntil, WAIT_FOREVER } from 'async-wait-until';
await waitUntil(() => someCondition, { timeout: WAIT_FOREVER });Adjust Retry Interval
Change how often the predicate is evaluated:
await waitUntil(() => someCondition, { intervalBetweenAttempts: 1000 }); // Check every 1 secondWait for API Response
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();
};Wait for File System Changes (Node.js)
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;
});Wait for Database Connection
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!');
};Wait with Custom Conditions
// 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)
CDN Usage
<!-- UMD bundle via CDN -->
<script src="https://unpkg.com/async-wait-until@latest/dist/index.js"></script>
<script>
// Available as global variable
asyncWaitUntil.waitUntil(() => document.querySelector('#target'))
.then(element => console.log('Found:', element));
</script>ES Modules in Browser
<script type="module">
import { waitUntil } from 'https://unpkg.com/async-wait-until@latest/dist/index.esm.js';
const element = await waitUntil(() => document.querySelector('#target'));
console.log('Found:', element);
</script>🔍 Troubleshooting
Common Issues
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_FOREVERwithout 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:
import { waitUntil, Options, TimeoutError } from 'async-wait-until';Performance Tips
- 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_FOREVERwith external cancellation for long-running waits
🧪 Development and Testing
Contributions are welcome! To contribute:
- Fork and clone the repository.
- Install dependencies:
npm install. 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