Angular-cli报错处理 You seem to not be depending on "@angular/core". This is an error.

按照官网执行
npm install -g @angular/cli
ng new my-app
cd my-app
ng serve –open
执行到最后一步却报错
E:\learnProject\angularDemo\firstAngular\my-app>ng serve --o
You seem to not be depending on "@angular/core". This is an error.
百度无果 总感觉是依赖包没有安装成功
于是，执行了
E:\learnProject\angularDemo\firstAngular\my-app>cnpm install

再次执行 ng serve –o 成功打开网页