Documentation should state that React preserves setState callback this context

I just recently found out that setState's callback calls with the correct this context per this line in the React source. Nowhere in the documentation is it stated that React internally calls callbacks with context. This should be made clear as many assume it doesn't, leading to unnecessary measures such as arrow functions, explicit binding, etc.

The lack of explicit documentation also creates confusion with other things that do require binding, such as traditional class methods used as event handlers.

從連結的 ReactFiberUpdateQueue.js 行開始，檢視現有的 setState callback 文件。完成的標準是文件明確說明 callback 會接收正確的 this context，並將這一點與作為事件處理常式使用的類別方法區分開來。