noPromiseExecutorReturn (JavaScript)

Language JavaScript (and super languages)

Summary

Rule available since: v2.6.0
Diagnostic Category: lint/nursery/noPromiseExecutorReturn
This rule has an unsafe fix.
The default severity of this rule is warning.
Sources:
- Same as no-promise-executor-return

How to configure

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{
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  "linter": {
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    "rules": {
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      "nursery": {
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        "noPromiseExecutorReturn": "error"
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      }
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    }
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  }
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}

Description

Disallow returning values from the function passed to new Promise().

When you create a Promise with new Promise(), you pass it a function called the executor. The executor usually starts an asynchronous task, such as reading a file. When the task finishes, the executor calls resolve with the result, or reject with an error.

new Promise() ignores the value that the executor returns, so returning a value has no effect on the Promise. This is usually a mistake: the code most likely meant to call resolve or reject instead.

A return statement without a value is allowed, because it only stops the executor early.

Examples

Invalid

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

code-block.js:3:9 lint/nursery/noPromiseExecutorReturn ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ⚠ The function passed to new Promise() returns a value here.
  
    1 │ new Promise((resolve, reject) => {
    2 │     if (someCondition) {
  > 3 │         return defaultResult;
      │         ^^^^^^^^^^^^^^^^^^^^^
    4 │     }
    5 │     getSomething((err, result) => {
  
  ℹ new Promise() ignores this returned value, so it has no effect on the Promise.
  
  ℹ Call resolve() or reject() to complete the Promise. To stop the function early, use return without a value.
  
  ℹ This rule belongs to the nursery group, which means it is not yet stable and may change in the future. Visit https://biomejs.dev/linter/#nursery for more information.

An arrow function without braces returns the value of its body:

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

code-block.js:1:34 lint/nursery/noPromiseExecutorReturn  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ⚠ The function passed to new Promise() returns this value.
  
  > 1 │ new Promise((resolve, reject) => getSomething((err, data) => {
      │                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  > 2 │     if (err) {
  > 3 │         reject(err);
  > 4 │     } else {
  > 5 │         resolve(data);
  > 6 │     }
  > 7 │ }));
      │ ^^
    8 │ 
  
  ℹ new Promise() ignores this returned value, so it has no effect on the Promise.
  
  ℹ Call resolve() or reject() to complete the Promise. To stop the function early, use return without a value.
  
  ℹ This rule belongs to the nursery group, which means it is not yet stable and may change in the future. Visit https://biomejs.dev/linter/#nursery for more information.
  
  ℹ Unsafe fix: Wrap the expression in braces.
  
    1   │ - new·Promise((resolve,·reject)·=>·getSomething((err,·data)·=>·{
      1 │ + new·Promise((resolve,·reject)·=>·{getSomething((err,·data)·=>·{
    2 2 │       if (err) {
    3 3 │           reject(err);
    ··· │ 
    5 5 │           resolve(data);
    6 6 │       }
    7   │ - }));
      7 │ + })});
    8 8 │

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

code-block.js:2:5 lint/nursery/noPromiseExecutorReturn ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ⚠ The function passed to new Promise() returns a value here.
  
    1 │ new Promise(() => {
  > 2 │     return 1;
      │     ^^^^^^^^^
    3 │ });
    4 │ 
  
  ℹ new Promise() ignores this returned value, so it has no effect on the Promise.
  
  ℹ Call resolve() or reject() to complete the Promise. To stop the function early, use return without a value.
  
  ℹ This rule belongs to the nursery group, which means it is not yet stable and may change in the future. Visit https://biomejs.dev/linter/#nursery for more information.

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new Promise(r => r(1));

code-block.js:1:18 lint/nursery/noPromiseExecutorReturn  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ⚠ The function passed to new Promise() returns this value.
  
  > 1 │ new Promise(r => r(1));
      │                  ^^^^
    2 │ 
  
  ℹ new Promise() ignores this returned value, so it has no effect on the Promise.
  
  ℹ Call resolve() or reject() to complete the Promise. To stop the function early, use return without a value.
  
  ℹ This rule belongs to the nursery group, which means it is not yet stable and may change in the future. Visit https://biomejs.dev/linter/#nursery for more information.
  
  ℹ Unsafe fix: Wrap the expression in braces.
  
    1 │ new·Promise(r·=>·{r(1)});
      │                  +    +

Valid

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new Promise((resolve, reject) => {
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    if (someCondition) {
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        resolve(defaultResult);
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        return;
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    }
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    getSomething((err, result) => {
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        if (err) {
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            reject(err);
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        } else {
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            resolve(result);
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        }
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    });
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});
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new Promise(r => { r(1) });
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Promise.resolve(1);