no-promise-executor-return

Disallow returning values from Promise executor functions

no-promise-executor-return

The executor function passed to new Promise should not return a value. The return value is ignored and returning a value is usually a mistake.

Rule Type: Problem
Fixable: No

Why This Rule Exists

The executor function of a Promise should call resolve() or reject() to settle the promise. The return value of the executor is ignored, so returning a value is pointless and usually indicates a misunderstanding of how Promises work.

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

Rule Details

This rule disallows returning values from Promise executor functions. Only return without a value (for control flow) is allowed.

Examples

Incorrect Code

// Returning a default value
new Promise((resolve, reject) => {
    if (someCondition) {
        return defaultResult; // Error: this value is ignored
    }
    getSomething((err, result) => {
        if (err) reject(err);
        else resolve(result);
    });
});

// Implicit return from arrow function
new Promise((resolve, reject) => getSomething((err, data) => {
    if (err) reject(err);
    else resolve(data);
})); // Error: getSomething's return value is ignored

// Explicit return value
new Promise(() => {
    return 1; // Error
});

// Arrow function implicit return
new Promise(r => r(1)); // Error: returns result of r(1)

Correct Code

// Use resolve instead of return
new Promise((resolve, reject) => {
    if (someCondition) {
        resolve(defaultResult); // Correct
        return; // OK: empty return for control flow
    }
    getSomething((err, result) => {
        if (err) reject(err);
        else resolve(result);
    });
});

// Add braces to prevent implicit return
new Promise((resolve, reject) => {
    getSomething((err, data) => {
        if (err) reject(err);
        else resolve(data);
    });
});

// Wrap body in braces
new Promise(r => { r(1); });

// Better: Use Promise.resolve for simple cases
Promise.resolve(1);

Common Patterns

Mixing Return with Resolve

Don’t confuse return with resolve(). They serve different purposes in Promise executors.

// Wrong: return doesn't settle the promise
new Promise((resolve, reject) => {
    if (condition) {
        return value; // Doesn't work!
    }
});

// Right: resolve settles the promise
new Promise((resolve, reject) => {
    if (condition) {
        resolve(value);
        return; // Optional: for control flow
    }
});

Arrow Function Gotchas

// Wrong: Implicit return
new Promise(resolve => doAsyncWork(resolve));

// Right: Explicit function body
new Promise(resolve => {
    doAsyncWork(resolve);
});

// Or use Promise wrapper
new Promise((resolve, reject) => {
    doAsyncWork()
        .then(resolve)
        .catch(reject);
});

// Better: Avoid Promise constructor entirely
function myPromise() {
    return doAsyncWork();
}

Early Exit Pattern

// Use empty return for early exit (this is OK)
new Promise((resolve, reject) => {
    if (cacheHit) {
        resolve(cachedValue);
        return; // Stop execution
    }
    
    fetchFromServer((err, data) => {
        if (err) reject(err);
        else resolve(data);
    });
});

Options

allowVoid

Type: boolean
Default: false

Allows returning void values (explicit void operator).

// With { "allowVoid": true }

// These are allowed:
new Promise((resolve, reject) => {
    if (someCondition) {
        return void resolve(defaultResult); // OK
    }
});

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

new Promise(r => void r(1)); // OK

The allowVoid option is useful if you prefer the explicit void operator to make it clear you’re intentionally discarding a return value.

Configuration

// Disallow all returns with values
{
  "rules": {
    "no-promise-executor-return": "error"
  }
}

// Allow void returns
{
  "rules": {
    "no-promise-executor-return": ["error", { 
      "allowVoid": true 
    }]
  }
}

Best Practices

1. Call resolve/reject, don’t return

// Wrong
new Promise((resolve) => {
    return value;
});

// Right
Promise.resolve(value);

2. Use Promise.resolve/reject for immediate values

// Unnecessary Promise constructor
new Promise(resolve => {
    resolve(value);
});

// Simpler
Promise.resolve(value);

3. Avoid the Promise constructor when possible

// Unnecessary wrapping
function getUser(id) {
    return new Promise((resolve, reject) => {
        fetch(`/api/user/${id}`)
            .then(resolve)
            .catch(reject);
    });
}

// Just return the promise directly
function getUser(id) {
    return fetch(`/api/user/${id}`);
}

4. Use async/await instead

// Complex Promise constructor
function getData() {
    return new Promise((resolve, reject) => {
        fetchUser((err, user) => {
            if (err) return reject(err);
            
            fetchPosts(user.id, (err, posts) => {
                if (err) return reject(err);
                resolve({ user, posts });
            });
        });
    });
}

// Cleaner with async/await
async function getData() {
    const user = await fetchUserPromise();
    const posts = await fetchPostsPromise(user.id);
    return { user, posts };
}

When Not to Use It

This rule should almost never be disabled. If you’re returning values from Promise executors, you likely have a bug or misunderstanding.

Related Rules

• no-async-promise-executor
• prefer-promise-reject-errors

Further Reading

• MDN: Promise Constructor