Compared with earlier versions, OpenHarmony 4.0.2.1 has the following API changes in its Web subsystem:
## cl.web.1 Parameter Type Change of postMessageEvent
The **postMessageEvent** API supported only the string type. In OpenHarmony 4.0.2.1 and later versions, it also supports the ArrayBuffer type.
**Change Impacts**
The API change is forward compatible. Applications developed based on earlier versions can still use the API, and the original functions are not affected.
**Key API/Component Changes**
- Involved APIs
postMessageEvent(message: string): void
- Before change
```ts
postMessageEvent(message:string):void
```
- After change
```ts
typeWebMessage=ArrayBuffer|string
postMessageEvent(message:WebMessage):void
```
**Adaptation Guide**
The API change is forward compatible. Applications developed based on earlier versions can still use the API, and the original functions are not affected.
## cl.web.2 Parameter Type Change of onMessageEvent
The **onMessageEvent** API supported only the string type. In OpenHarmony 4.0.2.1 and later versions, it also supports the ArrayBuffer type.
**Change Impacts**
The API change is forward compatible. Applications developed based on earlier versions can still use the API. With the corresponding logic handling added, the original functions are not affected.
The API change is forward compatible. Applications developed based on earlier versions can still use the API. With the corresponding logic handling added, the original functions are not affected.