Node.js 中有什么要求

Question

I was wondering how could an exported function that uses npm modules in it, run in another file which doesn't require these npm packages?

First file (which will be exported):

    const jwt = require("jsonwebtoken")
    var generateToken = function (){var token = jwt.sign({name:"medo"},"sas");return token}

    module.exports = generateToken

Second file (which will require the function):

    const token = require("./pack.js")
    console.log(token());

How does the function work successfully in the second file, when the jsonwebtoken module is not required in it?

Answer 1

It's a dependency tree. Your code loaded ./pack.js . In the process of loading that file, it then loaded the module jsonwebtoken . ./pack.js , then exports it's own function generateToken() and your code can then call generateToken() .

When generateToken() executes, it uses the jwt object that it previously imported in order to do its job.

The only thing that was successfully called from your file was the generateToken() function that was exported from ./pack.js . That gererateToken() function then executes in the scope of its own module where it has access to the things that it required in such as jwt .

---

Its analagous to what happens in operating system calls all the time. You call an operating system function to play an audio file. That operating system function then loads an appropriate sound driver (if not already loaded) and an appropriate codec for decompressing the type of sound file. Your code didn't have to load those things. You just called the OS function to play the sound file. It's the implementation of that function inside the OS that loads all the right pieces to actually carry out that function. Same in your nodejs example.