1# ForEach 2 3**ForEach** enables rendering of repeated content based on array type data. 4 5> **NOTE** 6> 7> The initial APIs of this module are supported since API version 7. Newly added APIs will be marked with a superscript to indicate their earliest API version. 8 9For details about the development, see [ForEach: Rendering Repeated Content](../../../ui/state-management/arkts-rendering-control-foreach.md). 10 11## APIs 12 13ForEach(arr: Array\<any\>, itemGenerator: (item: any, index: number) => void, keyGenerator?: (item: any, index: number) => string) 14 15**ForEach** enables rendering of repeated content based on array type data. It must be used in a container component, and the component it returns must be one allowed inside the container component. For example, for rendering of list items, **ForEach** must be used in the [List](../../../reference/apis-arkui/arkui-ts/ts-container-list.md) component. 16 17**Widget capability**: This API can be used in ArkTS widgets since API version 9. 18 19**Atomic service API**: This API can be used in atomic services since API version 11. 20 21**System capability**: SystemCapability.ArkUI.ArkUI.Full 22 23**Parameters** 24 25| Name | Type | Mandatory| Description | 26| ------------- | --------------------------------------- | ---- | ------------------------------------------------------------ | 27| arr | Array\<any\> | Yes | Data source, which is an array.<br>**NOTE**<br>- You can set this parameter to an empty array. In this case, no child component is created.<br>- You can also set this parameter to a function whose return value is an array, for example, **arr.slice (1, 3)**. However, the set function cannot change any state variables including the array itself. For example, **Array.splice**, **Array.sort**, and **Array.reverse** functions are not allowed, as they may change the array.| 28| itemGenerator | (item: any, index: number) => void | Yes | Component generator.<br>- It generates a component for each data item in an array. <br>- (Optional) **item**: data item in the **arr** array.<br>- (Optional) **index**: index of the data item in the **arr** array.<br>**NOTE**<br>- The type of the created component must be the one allowed inside the parent container component of **ForEach**. For example, a **ListItem** component is allowed only when the parent container component of **ForEach** is **List**.| 29| keyGenerator | (item: any, index: number) => string | No | Key generator.<br>- It generates a unique and persistent key for each array item of the data source **arr**. The return value is the key generation rule you customize.<br>- (Optional) **item**: data item in the **arr** array.<br>- (Optional) **index**: index of the data item in the **arr** array.<br>**NOTE**<br>- If this function is not specified, the default key generator of the framework is used: **(item: T, index: number) => { return index + '__' + JSON.stringify(item); }**.<br>- The key generator should not change any component state.| 30 31> **NOTE** 32> 33> - The **itemGenerator** function can contain an **if/else** statement, and an **if/else** statement can contain **ForEach**. 34> - On initial rendering, **ForEach** loads all data of the data source, creates a component for each data item, and mounts the created components to the render tree. If the data source contains a large number of items or performance is a critical concern, you are advised to use **LazyForEach**. For best practices, see [Performance Optimization Using LazyForEach](https://developer.huawei.com/consumer/en/doc/best-practices/bpta-lazyforeach-optimization). 35