> For the complete MongoDB documentation index, see www.mongodb.com/docs/llms.txt

# $type  (expression operator)

## Definition

Returns a string that specifies the [BSON type](https://www.mongodb.com/docs/manual/reference/bson-types.md#std-label-bson-types) of the argument.

[`$type`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/type.md#mongodb-expression-exp.-type) has the following [operator expression syntax:](https://www.mongodb.com/docs/manual/reference/mql/expressions.md#std-label-agg-quick-ref-operator-expressions)

```javascript
{ $type: <expression> }
```

The argument can be any valid [expression.](https://www.mongodb.com/docs/manual/reference/mql/expressions.md#std-label-aggregation-expressions)

**See also:**

- [`$isNumber`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/isnumber.md#mongodb-expression-exp.-isNumber) - checks if the argument is a number.

- [`$type (Query)`](https://www.mongodb.com/docs/manual/reference/operator/query/type.md#mongodb-query-op.-type) - filters fields based on BSON type.

## Behavior

### `$type`

Unlike the [`$type`](https://www.mongodb.com/docs/manual/reference/operator/query/type.md#mongodb-query-op.-type) query operator, which matches array elements based on their BSON type, the [`$type`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/type.md#mongodb-expression-exp.-type) aggregation operator does not examine array elements. Instead, when passed an array as its argument, the `$type` aggregation operator returns the type of the argument, i.e. `"array"`.

If the argument is a field that is missing in the input document, [`$type`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/type.md#mongodb-expression-exp.-type) returns the string `"missing"`.

The following table shows the [`$type`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/type.md#mongodb-expression-exp.-type) output for several common types of expressions:

| Example | Results |
| --- | --- |
| `{ $type: "a" }` | `"string"` |
| `{ $type: /a/ }` | `"regex"` |
| `{ $type: 1 }` | `"double"` |
| `{ $type: Long(627) }` | `"long"` |
| `{ $type: { x: 1 } }` | `"object"` |
| `{ $type: [ [ 1, 2, 3 ] ] }` | `"array"` |

**Note:**

In the case of a literal array such as `[ 1, 2, 3 ]`, enclose the expression in an outer set of array brackets to prevent MongoDB from parsing `[ 1, 2, 3 ]` as an [argument list](https://www.mongodb.com/docs/manual/reference/mql/expressions.md#std-label-agg-quick-ref-operator-expressions) with three arguments (`1, 2, 3`). Wrapping the array `[ 1, 2, 3 ]` in a [`$literal`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/literal.md#mongodb-expression-exp.-literal) expression achieves the same result.

See [operator expression syntax forms](https://www.mongodb.com/docs/manual/reference/mql/expressions.md#std-label-agg-quick-ref-operator-expressions) for more information.

### Available Types

| Type | Number | Alias | Notes |
| --- | --- | --- | --- |
| Double | 1 | "double" | |
| String | 2 | "string" | |
| Object | 3 | "object" | |
| Array | 4 | "array" | |
| Binary data | 5 | "binData" | |
| Undefined | 6 | "undefined" | Deprecated. |
| ObjectId | 7 | "objectId" | |
| Boolean | 8 | "bool" | |
| Date | 9 | "date" | |
| Null | 10 | "null" | |
| Regular Expression | 11 | "regex" | |
| DBPointer | 12 | "dbPointer" | Deprecated. |
| JavaScript | 13 | "javascript" | |
| Symbol | 14 | "symbol" | Deprecated. |
| JavaScript with scope | 15 | "javascriptWithScope" | Deprecated. |
| 32-bit integer | 16 | "int" | |
| Timestamp | 17 | "timestamp" | |
| 64-bit integer | 18 | "long" | |
| Decimal128 | 19 | "decimal" | |
| Min key | -1 | "minKey" | |
| Max key | 127 | "maxKey" | |

If the argument is a field that is missing in the input document, [`$type`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/type.md#mongodb-expression-exp.-type) returns the string `"missing"`.

## Example

This example uses a [collection](https://www.mongodb.com/docs/manual/reference/glossary.md#std-term-collection) named `coll` with the following [documents:](https://www.mongodb.com/docs/manual/reference/glossary.md#std-term-document)

```shell
db.coll.insertMany( [
   { _id: 0, a : 8 },
   { _id: 1, a : [ 41.63, 88.19 ] },
   { _id: 2, a : { a : "apple", b : "banana", c: "carrot" } },
   { _id: 3, a :  "caribou" },
   { _id: 4, a : Long(71) },
   { _id: 5, a : null },
   { _id: 6 }
] )
```

The following aggregation operation uses the `$type` operator to display the type of field `a` for all documents as part of the [`$project`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/project.md#mongodb-pipeline-pipe.-project) stage.

```shell
db.coll.aggregate([{
    $project: {
       a : { $type: "$a" }
    }
}])
```

**Output:**

```shell
[
   { _id: 0, "a" : "int" },
   { _id: 1, "a" : "array" },
   { _id: 2, "a" : "object" },
   { _id: 3, "a" : "string" },
   { _id: 4, "a" : "long" },
   { _id: 5, "a" : "null" },
   { _id: 6, "a" : "missing" }
]
```

### Existence Check

[Expressions](https://www.mongodb.com/docs/manual/reference/mql/expressions.md#std-label-aggregation-expressions) do not support the [`$exists`](https://www.mongodb.com/docs/manual/reference/operator/query/exists.md#mongodb-query-op.-exists) operator. To evaluate whether or not a field exists in an expression, you can use the `missing` type.

The following aggregation operation uses the `missing` type to add an `a` field to documents from the `coll` collection above that are missing the `a` field. Notice that a document where `a: null` is not the same as a document where the `a` field is missing.

```shell
db.coll.aggregate([  
  {  
    $addFields: {  
      a: {  
        $cond: {  
          if: { $eq: [{ $type: "$a" }, "missing"] },
          then: [], 
          else: "$a"
        }  
      }  
    }  
  }  
])  

```

**Output:**

```shell
[
   { _id: 0, a : 8 },
   { _id: 1, a : [ 41.63, 88.19 ] },
   { _id: 2, a : { a : "apple", b : "banana", c: "carrot" } },
   { _id: 3, a :  "caribou" },
   { _id: 4, a : Long(71) },
   { _id: 5, a : null },
   { _id: 6, a : [] }
]
```