Can't bind to 'ngModel' since it isn't a known property of 'input'

練習 Angular 時，使用雙向繫結 [(ngModel)]，會出現下面錯誤：

Can't bind to 'ngModel' since it isn't a known property of 'input'

這時要檢查 app.module.ts ，看看是否 import 了 FormsModule

https://angular.io/tutorial/toh-pt1#the-missing-formsmodule

官網上提到，當使用到雙向繫結關鍵字  [(ngModel)] 卻沒引用 FormsModule ，就會出現錯誤：

Can't bind to 'ngModel' since it isn't a known property of 'input'.

參考：Can't bind to 'ngModel' since it isn't a known property of 'input'