Several helper functions when working with native promises.
Useful for waiting a specific amount of time before continuing an operation.
import { sleep } from 'promise-assist';
async function myOperation() {
const startTime = Date.now();
await sleep(500);
console.log(`${Date.now() - startTime}ms passed!`);
}Useful for limiting the amount of time an async Promise-based operation can take.
import { timeout } from 'promise-assist';
async function myOperation() {
try {
const data = await timeout(
fetchDataFromServer(), // pass a Promise to the timeout function
10000, // request will be limited to 10 seconds
`failed loading required data from backend`
);
// do something with the data
} catch (e) {
// handle errors
}
}Creates a deferred Promise, where resolve/reject are exposed to the place that holds the promise.
Generally a bad practice, but there are use-cases, such as mixing callback-based and Promise-based APIs, where this is helpful.
import { deferred } from 'promise-assist';
const { promise, resolve, reject } = deferred<string>();
// `resolve` or `reject` calls are reflected on `promise`
promise.then((value) => console.log(value));
resolve('some text');
// 'some text' is printed to consoleExecutes provided action (sync or async) and returns its value.
If action throws or rejects, it will retry execution several times before failing.
Defaults are:
- 3 retries
- no delay between retries
- no timeout to stop trying
These can be customized via a second optional options parameter.
import { retry } from 'promise-assist';
// with default options
retry(() => fetch('http://some-url/asset.json'))
.then((value) => value.json())
.then(console.log)
.catch((e) => console.error(e));
// with custom options
retry(() => fetch('http://some-url/asset.json'), {
retries: Infinity, // infinite number of retries
delay: 10 * 1000, // 10 seconds delay between retries
timeout: 2 * 60 * 1000, // 2 minutes timeout to stop trying
})
.then((value) => value.json())
.then(console.log)
.catch((e) => console.error(e));Same as retry, but with defaults that make more sense for tests:
- delay:
10 - timeout:
1000 - retries:
Infinity
It can be used to wait for some assertion to pass.
import { waitFor } from 'promise-assist';
describe('suit', () => {
it('should wait for an assertion to pass', async () => {
let trueLater = false;
setTimeout(() => {
trueLater = true;
}, 50);
await waitFor(() => {
expect(trueLater).to.equal(true);
});
});
});MIT
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