node

1. node concepts

• http server + request router + request handler
• use DI everywhere, pass router/handler as parameter to server
• no 'return' is used, use async function, 'response' object is passed all the way to handler
• in node, any async function accepts a callback as the last parameter
• in node, any callback function accepts an error as the first parameter

2. even loop

• timer: execute timer callbacks
• pending callbacks: execute I/O callbacks
• poll: incoming I/O events and callbacks

3. npm config file

• ~/.npmrc

4. module.export and require

• module.export return an object
• require use the object

      module.exports = function(app, db) {};  // file1.js
      require('./app/routes')(app, {});               // file2.js

5. node/nvm commands

• node -v
• nvm --version
• nvm ls-remote
• nvm install x.x.x
• nvm uninstall x.x.x
• nvm use x.x.x
• nvm use node                                   //switch to latest
• nvm list
• nvm install --lts                                //install latest
• npm install -d                                   //--loglevel info
• npm install jsonpath --save-dev      //save it in package.json
• npm install -D jsonpath                   //-D is same as --save-dev
• npm init                                           //new node app, generate package.json
• node hello.js

6. node app config file

• ./config by default
• can be overwritten: process.env["NODE_CONFIG_DIR"] = __dirname + "/configDir/";

7. commonly lodash functions

• .find()

8. returning everything as objects of functions

const retryCounter = () => {
    let retryCounter = 0
    const totalRetry = 10 //config.get('errorHandler.retryTotal')

    return {
        retryTotal: () => {
            return totalRetry
        },
        count: () => {
            return retryCounter
        },
        add: () => {
            retryCounter += 1
        }
    }
}

9. print stack trace

• console.trace("Here I am!")

10. package-lock.json (normally more important than package.json, but)

• package.json overrule the package-lock.json if package.json has been updated
• 'npm install' sometimes does not update package-lock.json, better to use 'npm update' 
• version in package.json

major.minor.patch

1.0.2

~1.0.2 means to install version 1.0.2 or the latest patch version such as 1.0.4

^1.0.2 means to install version 1.0.2 or the latest minor or patch version such as 1.1.0

11. dependencies vs devDependencies

• dependencies is installed when using 'npm install' or 'npm install $package'
• devDependencies is installed when using 'npm install' or 'npm install --save-dev $package'
• dependencies is needed to run a package
• devDependencies is need to develop a package

reference

1. event loop
2. learn nodejs properly
3. nodejs best practice
4. build node.js API under 30 min
5. learn node in 3 days
6. build app using node and mongodb
7. configure your Node.js applications
8. node tutorial

9. everything you wanted to know about package-lock.json