> This attribute is supported since API version 7. Updates will be marked with a superscript to indicate their earliest API version.
> **NOTE**
>
> This event is supported since API version 7. Updates will be marked with a superscript to indicate their earliest API version.
## Required Permissions
...
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@@ -13,23 +15,23 @@ None
## Attributes
| Name | Type | Default Value | Description |
| Name| Type| Default Value| Description|
| -------- | -------- | -------- | -------- |
| visibility | Visibility | Visibility.Visible | Whether the component is shown or hidden. |
| visibility | Visibility | Visibility.Visible | Whether the component is visible. Note that even if a component is hidden, it needs to be re-created when the page is refreshed. Therefore, you are advised to use [conditional rendering](../../ui/ts-rending-control-syntax-if-else.md) instead under scenarios where consistently high performance is required. |
- Visibility enums
| Name | Description |
| Name| Description|
| -------- | -------- |
| Hidden | The component is hidden, and a placeholder is used for it in the layout. |
| Visible | The component is shown. |
| None | The component is hidden. It is not involved in the layout, and no placeholder is used for it. |
| Hidden | The component is hidden, and a placeholder is used for it in the layout.|
| Visible | The component is visible.|
| None | The component is hidden. It is not involved in the layout, and no placeholder is used for it.|
The development framework provides **ForEach** to iterate arrays and create components for each array item. If a large number of elements are involved in **ForEach**, the page loading may become slow. For best possible results, you are advised to use **[LazyForEach](ts-rending-control-syntax-lazyforeach.md)** instead. **ForEach** is defined as follows:
The development framework provides ForEach to iterate arrays and create components for each array item. ForEach is defined as follows:
| arr | any[] | Yes | - | Must be an array. An empty array is allowed. If an array is empty, no child component is created. You can set the functions whose return values are of the array type, for example, arr.slice (1, 3). The set functions cannot change any state variables including the array itself, such as Array.splice, Array.sort, and Array.reverse. |
| itemGenerator | (item: any, index?: number) => void | Yes | - | Used to generate the lambda function of the child components. It generates one or more child components for a given array item. A single component and its child component list must be contained in braces ({...}) |
| keyGenerator | (item: any, index?: number) => string | No | - | Used as an anonymous parameter for generating a unique and stable key value for a given array item. When the position of a subitem in the array is changed, the key value of the subitem cannot be changed. When a subitem in the array is replaced with a new item, the key value of the current item must be different from that of the new item. This key-value generator is optional. However, for performance reasons, it is strongly recommended that the key-value generator be provided, so that the development framework can better identify array changes. If the array is reversed while no key-value generator is provided, all nodes in ForEach will be rebuilt. |
| Name | Type | Mandatory | Default Value | Description |
| arr | any[] | Yes | - | Must be an array. An empty array is allowed. If the array is empty, no child component is created. The functions that return array-type values are also allowed, for example, **arr.slice (1, 3)**. The set functions cannot change any state variables including the array itself, such as **Array.splice**, **Array.sort**, and **Array.reverse**.|
| itemGenerator | (item: any, index?: number) => void | Yes | - | Lambda function used to generate one or more child components for a given array item. A component and its child component list must be enclosed in braces ({...}).|
| keyGenerator | (item: any, index?: number) => string | No | - | Anonymous parameter used to generate a unique and stable key value for a given array item. When the position of a subitem in the array is changed, the key value of the subitem cannot be changed. When a subitem in the array is replaced with a new item, the key value of the current item must be different from that of the new item. This key-value generator is optional. However, for performance reasons, it is strongly recommended that the key-value generator be provided, so that the development framework can better identify array changes. If the array is reversed while no key-value generator is provided, all nodes in **ForEach** will be rebuilt.|
> - The generated child components are allowed in the parent container component of ForEach. The child component generator function can contain the if/else conditional statement, and the if/else conditional statement can contain ForEach.
>
> - The calling sequence of subitem generator functions may be different from that of the data items in the array. During the development, do not assume whether the subitem generator and key value generator functions are executed and the execution sequence. The following is an example of incorrect usage:
>
> ```
> **NOTE**
> - **ForEach** must be used in container components.
>
> - The generated child components are allowed in the parent container component of **ForEach**. The child component generator function can contain the **if/else** conditional statement, and the **if/else** conditional statement can contain **ForEach**.
>
> - The call sequence of subitem generator functions may be different from that of the data items in the array. During the development, do not assume whether the subitem generator and key value generator functions are executed and the execution sequence. Below is an example of incorrect usage:
