> ## Documentation Index
> Fetch the complete documentation index at: https://mintlify.com/eslint/eslint/llms.txt
> Use this file to discover all available pages before exploring further.

# comma-dangle

> Require or disallow trailing commas

# comma-dangle

Trailing commas in object and array literals are valid in ES5 (and ES3). This rule enforces consistent use.

<Note>
  **Rule Type:** Layout\
  **Fixable:** Yes (automatically fixable)\
  **Deprecated:** Consider using Prettier
</Note>

## Why This Rule Exists

Trailing commas have advantages:

**Cleaner diffs:**

```diff theme={null}
// Without trailing comma
var foo = {
    bar: "baz",
-   qux: "quux"
+   qux: "quux",
+   added: "new"
};

// With trailing comma
var foo = {
    bar: "baz",
    qux: "quux",
+   added: "new",
};
```

**Easier refactoring:**

* Add/remove items by editing one line
* Less chance of syntax errors

## Rule Details

This rule enforces consistent trailing comma usage.

## Options

### String Option

* `"never"` (default) - Disallow trailing commas
* `"always"` - Require trailing commas
* `"always-multiline"` - Require when last element is on different line
* `"only-multiline"` - Allow but don't require when multiline

### Object Option

Configure for each syntax type:

```js theme={null}
{
  "comma-dangle": ["error", {
    "arrays": "never",
    "objects": "never",
    "imports": "never",
    "exports": "never",
    "functions": "never"
  }]
}
```

## Examples

### `"never"`

**Incorrect:**

```js theme={null}
var foo = {
    bar: "baz",
    qux: "quux",
};

var arr = [1,2,];

foo({
  bar: "baz",
  qux: "quux",
});
```

**Correct:**

```js theme={null}
var foo = {
    bar: "baz",
    qux: "quux"
};

var arr = [1,2];

foo({
  bar: "baz",
  qux: "quux"
});
```

### `"always"`

**Incorrect:**

```js theme={null}
var foo = {
    bar: "baz",
    qux: "quux"
};

var arr = [1,2];
```

**Correct:**

```js theme={null}
var foo = {
    bar: "baz",
    qux: "quux",
};

var arr = [1,2,];

foo({
  bar: "baz",
  qux: "quux",
},);
```

### `"always-multiline"`

<Tip>
  Most popular option - requires trailing commas for multiline, forbids for single-line.
</Tip>

**Incorrect:**

```js theme={null}
var foo = {
    bar: "baz",
    qux: "quux"
};

var foo = { bar: "baz", qux: "quux", };

var arr = [1,2,];

var arr = [
    1,
    2
];
```

**Correct:**

```js theme={null}
var foo = {
    bar: "baz",
    qux: "quux",
};

var foo = {bar: "baz", qux: "quux"};

var arr = [1,2];

var arr = [
    1,
    2,
];
```

### `"only-multiline"`

Allow but don't require trailing commas when multiline.

**Incorrect:**

```js theme={null}
var foo = { bar: "baz", qux: "quux", };
var arr = [1,2,];
```

**Correct:**

```js theme={null}
var foo = {
    bar: "baz",
    qux: "quux",
};

var foo = {
    bar: "baz",
    qux: "quux"
};

var foo = {bar: "baz", qux: "quux"};
var arr = [1,2];
```

### Functions

<Warning>
  Function trailing commas require ES2017+.
</Warning>

**Incorrect with `{"functions": "never"}`:**

```js theme={null}
function foo(a, b,) {
}

foo(a, b,);
new foo(a, b,);
```

**Correct:**

```js theme={null}
function foo(a, b) {
}

foo(a, b);
new foo(a, b);
```

## Configuration Examples

```js theme={null}
// Never use trailing commas
{
  "rules": {
    "comma-dangle": ["error", "never"]
  }
}

// Always use trailing commas
{
  "rules": {
    "comma-dangle": ["error", "always"]
  }
}

// Only for multiline (recommended)
{
  "rules": {
    "comma-dangle": ["error", "always-multiline"]
  }
}

// Different rules per type
{
  "rules": {
    "comma-dangle": ["error", {
      "arrays": "always-multiline",
      "objects": "always-multiline",
      "imports": "always-multiline",
      "exports": "always-multiline",
      "functions": "never"
    }]
  }
}
```

## When Not to Use It

<Tip>
  Most teams now use Prettier for formatting. If you use Prettier, disable this rule.
</Tip>

Disable if:

* You use Prettier or another formatter
* You need IE8 compatibility (very rare now)
* Your team hasn't agreed on trailing comma style

## Related Rules

* [comma-spacing](/rules/comma-spacing)
* [comma-style](/rules/comma-style)