nodejs看不到已安装的mysql模块

Question

I'm trying to install the mysql module for nodejs using npm. I'm using the windows subsystem for linux to do this. I've successfully installed using:

sudo npm install -g mysql

My console returns:

+ mysql@2.16.0
added 11 packages from 15 contributors in 5.779s

However, when importing the module using:

const mysql = require("mysql"); 

I receive the error:

module.js:550
    throw err;
    ^

Error: Cannot find module 'mysql'
    at Function.Module._resolveFilename (module.js:548:15)
    at Function.Module._load (module.js:475:25)
    at Module.require (module.js:597:17)
    at require (internal/module.js:11:18)
    at Object.<anonymous> (/mnt/c/Users/alesi/Documents/coding/Web/Portfolio/src/servers/server.js:7:15)
    at Module._compile (module.js:653:30)
    at Object.Module._extensions..js (module.js:664:10)
    at Module.load (module.js:566:32)
    at tryModuleLoad (module.js:506:12)
    at Function.Module._load (module.js:498:3)

Other modules such as querystring and nodemailer work just fine. Any ideas?

Answer 1

When you install a package globally, the package is usually installed in %USERPROFILE%\\AppData\\Roaming\\npm\\node_module on windows or /usr/local/lib/node_modules in unix systems. See this post.

Now in your project, when you require() something, it is looking to the current directory's node_modules folder. Because you installed the package globally, it does not exist in the project.

Running this will download the package to your project's node_modules folder, instead of global node_modules . --save will also write it as a dependency to package.json

npm install --save mysql

In my experience, global packages seem to be used for CLI's or running scripts from command prompt, and not for using in code.