什么是process.env。港口在node . js ?

what is process.env.PORT || 3000 used for in Node.js? I saw this somewhere:

什么是process.env。端口|| 3000在Node.js中使用。我看到这个地方:

 app.set('port', process.env.PORT || 3000);

If it is used to set 3000 as the listening port, can I use this instead?

如果用3000作为监听端口，我可以用这个吗?

app.listen(3000);

If not why?

如果不是为什么?

4 个解决方案

#1

155

In many environments (e.g. Heroku), and as a convention, you can set the environment variable PORT to tell your web server what port to listen on.

在许多环境中(例如Heroku)，作为一种约定，您可以设置环境变量端口来告诉web服务器监听哪个端口。

So process.env.PORT || 3000 means: whatever is in the environment variable PORT, or 3000 if there's nothing there.

所以process.env。|| 3000的意思是:无论环境变量端口是什么，或者3000，如果没有的话。

So you pass that app.listen, or to app.set('port', ...), and that makes your server be able to accept a parameter from the environment what port to listen on.

因此，您将该app.listen或app.set('port'，…)传递给它，这使您的服务器能够从环境中接受要侦听的端口的参数。

If you pass 3000 hard-coded to app.listen(), you're always listening on port 3000, which might be just for you, or not, depending on your requirements and the requirements of the environment in which you're running your server.

如果您将3000硬编码传递给app.listen()，您总是在监听端口3000，这可能只针对您，也可能不针对您，这取决于您的需求和运行服务器的环境的需求。

#2

if you run node index.js ,Node will use 3000

如果运行节点索引。js，节点将使用3000。
If you run PORT=4444 node index.js, Node will use process.env.PORT which equals to 4444 in this example. Run with sudo for ports below 1024.

如果运行端口=4444节点索引。Node将使用process.env。端口在这个例子中等于4444。对1024以下的端口运行sudo。

#3

When hosting your application on another service (like Heroku, Nodejitsu, and AWS), your host may independently configure the process.env.PORT variable for you; after all, your script runs in their environment.

当在另一个服务(如Heroku、Nodejitsu和AWS)上托管应用程序时，主机可以独立配置process.env。为你端口变量;毕竟，您的脚本在它们的环境中运行。

Amazon's Elastic Beanstalk does this. If you try to set a static port value like 3000 instead of process.env.PORT || 3000 where 3000 is your static setting, then your application will result in a 500 gateway error because Amazon is configuring the port for you.

亚马逊的弹性豆茎可以做到这一点。如果您试图将静态端口值设置为3000而不是process.env。端口|| 3000，其中3000是您的静态设置，那么您的应用程序将导致500个网关错误，因为Amazon正在为您配置端口。

This is a minimal Express application that will deploy on Amazon's Elastic Beanstalk:

这是一个将部署在Amazon的弹性Beanstalk上的最小Express应用程序:

var express = require('express');
var app = express();

app.get('/', function (req, res) {
  res.send('Hello World!');
});

// use port 3000 unless there exists a preconfigured port
var port = process.env.port || 3000;

app.listen(port);

#4

In some scenarios, port can only be designated by the environment and is saved in a user environment variable. Below is how node.js apps work with it.

在某些场景中，端口只能由环境指定，并保存在用户环境变量中。下面是如何节点。js应用程序可以使用它。

The process object is a global that provides information about, and control over, the current Node.js process. As a global, it is always available to Node.js applications without using require().

流程对象是提供关于当前节点的信息和控制的全局对象。js的过程。作为一个全局变量，节点总是可用的。不使用require()的js应用程序。

The process.env property returns an object containing the user environment.

这个过程。env属性返回一个包含用户环境的对象。

An example of this object looks like:

这个对象的一个例子如下:

{
  TERM: 'xterm-256color',
  SHELL: '/usr/local/bin/bash',
  USER: 'maciej',
  PATH: '~/.bin/:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin',
  PWD: '/Users/maciej',
  EDITOR: 'vim',
  SHLVL: '1',
  HOME: '/Users/maciej',
  LOGNAME: 'maciej',
  _: '/usr/local/bin/node'
}

For example,

例如,

terminal: set a new user environment variable, not permanently

终端:设置一个新的用户环境变量，不是永久的

export MY_TEST_PORT=9999

app.js: read the new environment variable from node app

js:从node app中读取新的环境变量

console.log(process.env.MY_TEST_PORT)

terminal: run the node app and get the value

终端:运行节点app获取值

$ node app.js
9999

#1

155