How to specify the entry file in nodejs (a brief analysis of multiple methods)

Node.js is a JavaScript runtime environment based on the Chrome V8 engine that can build highly scalable web applications on the server side. In Node.js, each file is considered a module, and each module can independently export its own methods and properties for use by other modules.

However, in actual development, it is often necessary to specify a file as the entry point of the program. Node.js provides multiple methods to specify entry files, which will be introduced one by one with code examples below.

Default entry file

When we run a folder through the node command, Node.js will automatically look for index.js# under the folder. ##, index.json or index.node file, and use this file as the entry point of the program. For example, in a folder named app, there is a index.js file. We can start the program with the following command:

node app

At this time, Node .js will automatically look for the

index.js file in the app folder and execute the code in it.

Specify the entry file in package.json

If our program needs to depend on some third-party modules (for example, Express.js, socket.io, etc.), we can specify it in

package. Define these dependencies in the json file and specify the entry file of the program.

{
  "name": "my-app",
  "version": "1.0.0",
  "description": "My Application",
  "main": "app.js", // 指定入口文件
  "dependencies": {
    "express": "^4.17.1",
    "socket.io": "^4.2.0"
  }
}

In the above

package.json file, the main field specifies that the entry file of the program is app.js, that is, at startup The code in app.js will be executed when the program is executed.

Command line parameter transfer entry file

In addition to the default

index.js and package.json specified entry file, we can also pass the command line parameters to manually specify the entry file.

node my-app.js

In the above command, we manually specified

my-app.js as the entry file of the program. This method is suitable for situations where multiple entry files need to be executed in the same folder.

require method to specify the entry file

Finally, we can also specify the entry file through the

require method.

require('./app.js');

In the above code, we loaded the

app.js file through the require method and used it as the entry file of the program. This method is suitable for situations where you need to perform some operations on the file (for example, setting global variables, modifying module variables, etc.) before it can be executed as an entry file.

In short, the above are several ways to specify the entry method in Node.js. We can choose according to the actual situation. In actual development, we may combine these methods. For example, specify the entry file in

package.json and perform the initialization operation of the third-party module in this file.

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