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

# $allElementsTrue (expression operator)

## Definition

Evaluates an array as a set and returns `true` if *no* element in the array is `false`. Otherwise, returns `false`. An empty array returns `true`.

[`$allElementsTrue`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/allelementstrue.md#mongodb-expression-exp.-allElementsTrue) has the following syntax:

```javascript
{ $allElementsTrue: [ <expression> ] }
```

The `<expression>` itself must resolve to an array, separate from the outer array that denotes the argument list. For more information on expressions, see [Expressions.](https://www.mongodb.com/docs/manual/reference/mql/expressions.md#std-label-aggregation-expressions)

## Behavior

If a set contains a nested array element, [`$allElementsTrue`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/allelementstrue.md#mongodb-expression-exp.-allElementsTrue) does *not* descend into the nested array but evaluates the array at top-level.

In addition to the `false` boolean value, [`$allElementsTrue`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/allelementstrue.md#mongodb-expression-exp.-allElementsTrue) evaluates as `false` the following: `null`, `0`, and `undefined` values. The [`$allElementsTrue`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/allelementstrue.md#mongodb-expression-exp.-allElementsTrue) evaluates all other values as `true`, including non-zero numeric values and arrays.

| Example | Result |
| --- | --- |
| `{ $allElementsTrue: [ [ true, 1, "someString" ] ] }` | `true` |
| `{ $allElementsTrue: [ [ [ false ] ] ] }` | `true` |
| `{ $allElementsTrue: [ [ ] ] }` | `true` |
| `{ $allElementsTrue: [ [ null, false, 0 ] ] }` | `false` |

## Example

Create an example collection named `survey` with the following documents:

```javascript
db.survey.insertMany([
   { "_id" : 1, "responses" : [ true ] },
   { "_id" : 2, "responses" : [ true, false ] },
   { "_id" : 3, "responses" : [ ] },
   { "_id" : 4, "responses" : [ 1, true, "seven" ] },
   { "_id" : 5, "responses" : [ 0 ] },
   { "_id" : 6, "responses" : [ [ ] ] },
   { "_id" : 7, "responses" : [ [ 0 ] ] },
   { "_id" : 8, "responses" : [ [ false ] ] },
   { "_id" : 9, "responses" : [ null ] },
   { "_id" : 10, "responses" : [ undefined ] }
])
```

The following operation uses the [`$allElementsTrue`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/allelementstrue.md#mongodb-expression-exp.-allElementsTrue) operator to determine if the `responses` array only contains values that evaluate to `true`:

```javascript
db.survey.aggregate(
   [
     { $project: { responses: 1, isAllTrue: { $allElementsTrue: [ "$responses" ] }, _id: 0 } }
   ]
)
```

The operation returns the following results:

```javascript
{ "responses" : [ true ], "isAllTrue" : true }
{ "responses" : [ true, false ], "isAllTrue" : false }
{ "responses" : [ ], "isAllTrue" : true }
{ "responses" : [ 1, true, "seven" ], "isAllTrue" : true }
{ "responses" : [ 0 ], "isAllTrue" : false }
{ "responses" : [ [ ] ], "isAllTrue" : true }
{ "responses" : [ [ 0 ] ], "isAllTrue" : true }
{ "responses" : [ [ false ] ], "isAllTrue" : true }
{ "responses" : [ null ], "isAllTrue" : false }
{ "responses" : [ undefined ], "isAllTrue" : false }
```