@putout/plugin-promises
v16.0.0
Published
🐊Putout plugin improves Promise-related code
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@putout/plugin-promises
A
Promise
is in one of these states:
- ✅
pending
: initial state, neither fulfilled nor rejected;- ✅
fulfilled
: meaning that the operation was completed successfully;- ✅
rejected
: meaning that the operation failed;(c) MDN
🐊Putout plugin improves Promise
-related code.
Install
npm i @putout/plugin-promises -D
Rules
- ✅ add-missing-async;
- ✅ add-missing-await;
- ✅ apply-await-import;
- ✅ apply-top-level-await;
- ✅ apply-with-resolvers;
- ✅ convert-new-promise-to-async;
- ✅ convert-reject-to-throw;
- ✅ remove-useless-async;
- ✅ remove-useless-await;
- ✅ remove-useless-resolve;
- ✅ remove-useless-variables;
Config
{
"rules": {
"promises/add-missing-await": "on",
"promises/add-missing-async": "on",
"promises/apply-await-import": "on",
"promises/apply-top-level-await": "on",
"promises/apply-with-resolvers": "off",
"promises/remove-useless-resolve": "on",
"promises/remove-useless-async": "on",
"promises/remove-useless-await": "on",
"promises/remove-useless-variables": "on",
"promises/convert-reject-to-throw": "on",
"promises/convert-new-promise-to-async": "on"
}
}
☝️ If you want to override any of it, update .putout.json
in the directory near your files.
🦉 Configuration section of 🐊Putout documentation tell you more about all configuration options supported.
apply-await-import
add forgotten await to dynamic import()
.
❌ Example of incorrect code
const {readFile} = import('node:fs/promises');
✅ Example of correct code
const {readFile} = await import('node:fs/promises');
apply-with-resolvers
The
Promise.withResolvers()
static method returns an object containing a newPromise
object and two functions toresolve
orreject
it, corresponding to the two parameters passed to the executor of thePromise()
constructor.(c) MDN
Checkout in
❌ Example of incorrect code
const promise = new Promise((res, rej) => {});
✅ Example of correct code
const {
promise,
resolve,
reject,
} = Promise.withResolvers();
remove-useless-resolve
❌ Example of incorrect code
async function hello() {
return Promise.resolve('hello');
}
✅ Example of correct code
async function hello() {
return 'hello';
}
remove-useless-async
❌ Example of incorrect code
async function hello() {
return 'hello';
}
✅ Example of correct code
function hello() {
return 'hello';
}
remove-useless-await
If a handler function returns another pending promise object, the resolution of the promise returned by
then
will be subsequent to the resolution of the promise returned by the handler. Also, the resolved value of the promise returned bythen
will be the same as the resolved value of the promise returned by the handler.(c) MDN
❌ Example of incorrect code
await await Promise.resolve();
const hello = await 'world';
✅ Example of correct code
await Promise.resolve();
const hello = 'world';
convert-reject-to-throw
❌ Example of incorrect code
async function hello() {
return Promise.reject(Error('error'));
}
✅ Example of correct code
async function hello() {
throw Error('error');
}
add-missing-await
Using
return await
inside anasync function
keeps the currentfunction
in thecall stack
until thePromise
that is being awaited has resolved, at the cost of an extra microtask before resolving the outerPromise
.return await
can also be used in atry/catch statement
to catch errors from another function that returns a Promise.
You can avoid the extra microtask by not awaiting the return value, with the trade off of the function no longer being a part of the stack trace if an error is thrown asynchronously from the
Promise
being returned. This can make debugging more difficult.(c) ESLint
❌ Example of incorrect code
runCli();
async function runCli() {}
✅ Example of correct code
await runCli();
async function runCli() {}
add-missing-async
The
async
function declaration creates a binding of a new async function to a given name. Theawait
keyword is permitted within the function body, enabling asynchronous, promise-based behavior to be written in a cleaner style and avoiding the need to explicitly configure promise chains.(c) MDN
❌ Example of incorrect code
function hello() {
await world();
}
✅ Example of correct code
async function hello() {
await world();
}
convert-new-promise-to-async
❌ Example of incorrect code
function get() {
return new Promise((resolve, reject) => {
reject(Error('Cannot get'));
});
}
✅ Example of correct code
async function get() {
throw Error('Cannot get');
}
apply-top-level-await
Applies top-level-await.
❌ Example of incorrect code
import {readFile} from 'node:fs/promises';
(async () => {
await readFile('./README.md', 'utf8');
})();
✅ Example of correct code
import {readFile} from 'node:fs/promises';
await readFile('./README.md', 'utf8');
remove-useless-variables
❌ Example of incorrect code
async () => {
const result = transformer.transform(realTransformer, transformCode, code, parser);
const result2 = await Promise.resolve(result);
return result2;
};
✅ Example of correct code
async () => {
const result = transformer.transform(realTransformer, transformCode, code, parser);
return result;
};
License
MIT