Wait for a condition to be true
Can be useful for polling.
npm install p-wait-forimport pWaitFor from 'p-wait-for';
import {pathExists} from 'path-exists';
await pWaitFor(() => pathExists('unicorn.png'));
console.log('Yay! The file now exists.');Returns a Promise that resolves when condition returns true. Rejects if condition throws or returns a Promise that rejects.
Type: Function
Expected to return Promise<boolean> | boolean.
Type: object
Type: number
Default: 20
Number of milliseconds to wait after condition resolves to false before calling it again.
Type: number | TimeoutOptions
Default: Infinity
Number of milliseconds to wait before automatically rejecting with a TimeoutError.
You can customize the timeout Error by specifying TimeoutOptions.
import pWaitFor from 'p-wait-for';
import {pathExists} from 'path-exists';
const originalSetTimeout = setTimeout;
const originalClearTimeout = clearTimeout;
sinon.useFakeTimers();
await pWaitFor(() => pathExists('unicorn.png'), {
timeout: {
milliseconds: 100,
message: new MyError('Time’s up!'),
customTimers: {
setTimeout: originalSetTimeout,
clearTimeout: originalClearTimeout
}
}
});
console.log('Yay! The file now exists.');Type: number
Default: Infinity
Milliseconds before timing out.
Passing Infinity will cause it to never time out.
Type: string | Error
Default: 'Promise timed out after 50 milliseconds'
Specify a custom error message or error.
If you do a custom error, it's recommended to sub-class TimeoutError.
Type: object with function properties setTimeout and clearTimeout
Custom implementations for the setTimeout and clearTimeout functions.
Useful for testing purposes, in particular to work around sinon.useFakeTimers().
Type: Function
Do something other than rejecting with an error on timeout.
Example:
import pWaitFor from 'p-wait-for';
import {pathExists} from 'path-exists';
await pWaitFor(() => pathExists('unicorn.png'), {
timeout: {
milliseconds: 50,
fallback: () => {
console.log('Time’s up! executed the fallback function!');
},
}
});Type: boolean
Default: true
Whether to run the check immediately rather than starting by waiting interval milliseconds.
Useful for when the check, if run immediately, would likely return false. In this scenario, set before to false.
Resolve the main promise with a custom value.
import pWaitFor from 'p-wait-for';
import pathExists from 'path-exists';
const path = await pWaitFor(async () => {
const path = getPath();
return await pathExists(path) && pWaitFor.resolveWith(path);
});
console.log(path);Exposed for instance checking.