Disallow returning values from Promise executor functions (no-promise-executor-return)

The new Promise constructor accepts a single argument, called an executor.

const myPromise = new Promise(function executor(resolve, reject) {
    readFile('foo.txt', function(err, result) {
        if (err) {
            reject(err);
        } else {
            resolve(result);
        }
    });
});

The executor function usually initiates some asynchronous operation. Once it is finished, the executor should call resolve with the result, or reject if an error occurred.

The return value of the executor is ignored. Returning a value from an executor function is a possible error because the returned value cannot be used and it doesn't affect the promise in any way.

Rule Details

This rule disallows returning values from Promise executor functions.

Only return without a value is allowed, as it's a control flow statement.

Examples of incorrect code for this rule:

/*eslint no-promise-executor-return: "error"*/

new Promise((resolve, reject) => {
    if (someCondition) {
        return defaultResult;
    }
    getSomething((err, result) => {
        if (err) {
            reject(err);
        } else {
            resolve(result);
        }
    });
});

new Promise((resolve, reject) => getSomething((err, data) => {
    if (err) {
        reject(err);
    } else {
        resolve(data);
    }
}));

new Promise(() => {
    return 1;
});

Examples of correct code for this rule:

/*eslint no-promise-executor-return: "error"*/

new Promise((resolve, reject) => {
    if (someCondition) {
        resolve(defaultResult);
        return;
    }
    getSomething((err, result) => {
        if (err) {
            reject(err);
        } else {
            resolve(result);
        }
    });
});

new Promise((resolve, reject) => {
    getSomething((err, data) => {
        if (err) {
            reject(err);
        } else {
            resolve(data);
        }
    });
});

Promise.resolve(1);

Further Reading

Version

This rule was introduced in ESLint 7.3.0.

Resources