# Observer

**Description:**

  A record representing an observer of entity changes in the game systems.

**Class Object:** [Observer Class](/docs/api/Class%20Object/Observer).

## watch

**Type:** Function.

**Description:**

  Watches the components changes to entities that match the observer's component filter.

**Signature:**
```tl
watch: function(self: Observer, func: function(Entity): boolean): Observer
```

**Parameters:**

| Parameter | Type | Description |
| --- | --- | --- |
| func | function | The function to call when a change occurs. Returns true to stop watching. |

**Returns:**

| Return Type | Description |
| --- | --- |
| Observer | The same observer, for method chaining. |