Installing安装

Assuming you’ve already installed Node.js, create a directory to hold your application, and make that your working directory.假设您已经安装了Node.js，创建一个目录来保存应用程序，并将其设置为工作目录。

$ mkdir myapp
$ cd myapp

Use the npm init command to create a package.json file for your application.使用npm init命令为应用程序创建package.json文件。 For more information on how package.json works, see Specifics of npm’s package.json handling.有关package.json如何工作的更多信息，请参阅npm的package.json处理细节。

$ npm init

This command prompts you for a number of things, such as the name and version of your application.此命令会提示您输入许多内容，例如应用程序的名称和版本。For now, you can simply hit RETURN to accept the defaults for most of them, with the following exception:目前，您只需点击RETURN键即可接受大多数默认值，但以下情况除外：

entry point: (index.js)

Enter app.js, or whatever you want the name of the main file to be.输入app.js或任何您想要的主文件名。If you want it to be index.js, hit RETURN to accept the suggested default file name.如果希望它是index.js，请单击RETURN接受建议的默认文件名。

Now install Express in the myapp directory and save it in the dependencies list.现在在myapp目录中安装Express，并将其保存在依赖项列表中。For example:例如：

$ npm install express --save

To install Express temporarily and not add it to the dependencies list:要临时安装Express而不将其添加到依赖项列表，请执行以下操作：

$ npm install express --no-save

Next: Hello World