September 2022
Intermediate to advanced
585 pages
8h 17m
Chinese
Content preview from JavaScript 经典实例：第三版
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499
第
19
章
管理
Node
Node
生态系统覆盖广泛，从在笔记本电脑中运行脚本，到管理远程服务器上的数据，
一应俱全。
Node
核心功能丰富多样，加上用户创建的数千个模块，为几乎任何编程
任务提供了丰富的环境。然而，这种多样性也给常见任务带来了一定的挑战，毕竟
选项太多。本章说明
Node
开发人员可能面对的一些常见问题。
19.1
使用环境变量
19.1.1
问题
你的
Node
应用需要在不同的环境（例如本地设备和生产环境）中使用不同的值。
19.1.2
方案
使用环境变量在不同的环境中设定和读取值。
Node
核心模块
process
中有一个
env
属性，应用通过它可以访问任何环境变量。下述示例读取一个名为
NODE_ENV
的环
境变量。
process.env.NODE_ENV
若想设定环境变量，在运行启动应用的
node
命令之前为变量指定一个值。下述命令
把
NODE_ENV
的值设为
development
，然后运行
index.js
脚本。
500
｜
第
19
章
$ NODE_ENV=development node index.js
如果项目使用多个环境变量，通常把环境变量的值存储在本地的
.env
文件中。在
Node
应用中，如果想这么做，要使用
npm
安装
dotenv
包。
$ npm install dotenv --save
现在，在应用代码中，引入该模块并加载配置。 ...
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I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.