eslint-plugin-promise
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The eslint-plugin-promise package is an ESLint plugin that enforces best practices and common idioms for dealing with promises in JavaScript. It provides a set of rules that catch common mistakes and enforce conventions when working with promises.
Avoiding creation of new promises outside of utility libraries
This rule ensures that the executor function of a new Promise has the parameters named 'resolve' and 'reject'.
/* eslint promise/param-names: 'error' */
new Promise((resolve, reject) => { /* executor function */ });Ensuring that each time a then() is applied to a promise, a catch() is applied as well
This rule enforces the use of catch() on unhandled promises.
/* eslint promise/catch-or-return: 'error' */
promise.then(function(data) {
// handle data
}).catch(function(error) {
// handle error
});Enforcing the return of a promise in certain contexts
This rule ensures that promise chains always return a value, preventing silent failures and unhandled rejections.
/* eslint promise/always-return: 'error' */
function foo() {
return doSomething().then(function() {
// do something else
return 'result';
});
}This plugin provides ESLint rules for async/await syntax, which is related to promises. It helps to enforce best practices and catch common mistakes when using async/await, but it does not focus on promises directly.
Part of the 'eslint-plugin-standard' plugin includes rules that are applicable to promises, as it adheres to the JavaScript Standard Style. However, it covers a broader range of JavaScript features and is not solely focused on promises.
Enforce best practices for JavaScript promises.
You'll first need to install ESLint:
$ npm i eslint --save-dev
Next, install eslint-plugin-promise:
$ npm install eslint-plugin-promise --save-dev
Note: If you installed ESLint globally (using the -g flag) then you must also install eslint-plugin-promise globally.
Add promise to the plugins section of your .eslintrc configuration file. You can omit the eslint-plugin- prefix:
{
"plugins": [
"promise"
]
}
Then configure the rules you want to use under the rules section.
{
"rules": {
"promise/always-return": "error",
"promise/no-return-wrap": "error",
"promise/param-names": "error",
"promise/catch-or-return": "error",
"promise/no-native": "off",
"promise/no-nesting": "warn",
"promise/no-promise-in-callback": "warn",
"promise/no-callback-in-promise": "warn",
"promise/avoid-new": "warn"
}
}
catch-or-return Enforces the use of catch on un-returned promises.no-return-wrap Avoid wrapping values in Promise.resolve or Promise.reject when not needed.param-names Enforce consistent param names when creating new promises.always-return Return inside each then to create readable and reusable Promise chains.no-native In an ES5 environment, make sure to create a Promise constructor before using.no-nesting Avoid nested .then() or .catch() statementsno-promise-in-callback Avoid using promises inside of callbacksno-callback-in-promise Avoid calling cb() inside of a then() (use nodeify] instead)avoid-new Avoid creating new promises outside of utility libs (use pify instead)prefer-await-to-then Prefer await to then() for reading Promise valuesprefer-await-to-callbacks Prefer async/await to the callback patterncatch-or-returnEnsure that each time a then() is applied to a promise, a
catch() is applied as well. Exceptions are made if you are
returning that promise.
myPromise.then(doSomething).catch(errors);
myPromise.then(doSomething).then(doSomethingElse).catch(errors);
function doSomethingElse() { return myPromise.then(doSomething) }
myPromise.then(doSomething);
myPromise.then(doSomething, catchErrors); // catch() may be a little better
function doSomethingElse() { myPromise.then(doSomething) }
allowThenYou can pass an { allowThen: true } as an option to this rule
to allow for .then(null, fn) to be used instead of catch() at
the end of the promise chain.
terminationMethodYou can pass a { terminationMethod: 'done' } as an option to this rule
to require done() instead of catch() at the end of the promise chain.
This is useful for many non-standard Promise implementations.
You can also pass an array of methods such as
{ terminationMethod: ['catch', 'asCallback', 'finally'] }.
This will allow any of
Promise.resolve(1).then(() => { throw new Error('oops') }).catch(logerror)
Promise.resolve(1).then(() => { throw new Error('oops') }).asCallback(cb)
Promise.resolve(1).then(() => { throw new Error('oops') }).finally(cleanUp)
always-returnEnsure that inside a then() you make sure to return a new promise or value.
See http://pouchdb.com/2015/05/18/we-have-a-problem-with-promises.html (rule #5)
for more info on why that's a good idea.
We also allow someone to throw inside a then() which is essentially the same as return Promise.reject().
myPromise.then((val) => val * 2));
myPromise.then(function(val) { return val * 2; });
myPromise.then(doSomething); // could be either
myPromise.then((b) => { if (b) { return "yes" } else { return "no" } });
myPromise.then(function(val) {});
myPromise.then(() => { doSomething(); });
myPromise.then((b) => { if (b) { return "yes" } else { forgotToReturn(); } });
param-namesEnforce standard parameter names for Promise constructors
new Promise(function (resolve) { ... })
new Promise(function (resolve, reject) { ... })
new Promise(function (reject, resolve) { ... }) // incorrect order
new Promise(function (ok, fail) { ... }) // non-standard parameter names
Ensures that new Promise() is instantiated with the parameter names resolve, reject to avoid confusion with order such as reject, resolve. The Promise constructor uses the RevealingConstructor pattern. Using the same parameter names as the language specification makes code more uniform and easier to understand.
no-nativeEnsure that Promise is included fresh in each file instead of relying
on the existence of a native promise implementation. Helpful if you want
to use bluebird or if you don't intend to use an ES6 Promise shim.
var Promise = require("bluebird");
var x = Promise.resolve("good");
var x = Promise.resolve("bad");
no-return-wrapEnsure that inside a then() or a catch() we always return
or throw a raw value instead of wrapping in Promise.resolve
or Promise.reject
myPromise.then(function(val) {
return val * 2;
});
myPromise.then(function(val) {
throw "bad thing";
});
myPromise.then(function(val) {
return Promise.resolve(val * 2);
});
myPromise.then(function(val) {
return Promise.reject("bad thing");
})
3.4.2
FAQs
Enforce best practices for JavaScript promises
The npm package eslint-plugin-promise receives a total of 4,108,108 weekly downloads. As such, eslint-plugin-promise popularity was classified as popular.
We found that eslint-plugin-promise demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 2 open source maintainers collaborating on the project.
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