• What is express?
  • https://expressjs.com/en/5x/api.html#app.post.method
  • Express is a "fast, unopinionated, minimalist web framework for Node.js:"  It helps us build web apps!
  • It's just an NPM package which comes with a bunch of methods and optional plugins that we can use to build web applications and API's
• Express help us:
  • Start up a server to listen for requests
  • Parse incoming requests
  • Match those requests to particular routes
  • Craft our http response and associated content
• Libraries VS frameworks
  • library: When you use a library, you are in charge! You control the flow of the application code, and you decide when to use the library.
  • framework: With frameworks, that control is inverted.  The framework is in charge, and you are merely a participant! The framework tells you where to plug in the code.
• Templating
  • Templating allows us to define a preset "pattern" for a webpage, that we can dynamically modify.
  • For example, we could define a single "Search" template that displays all the results for a given search term.  We don't know what the term is or how many results there are ahead of time.  The webpage is created on the fly.
• start with express
  1. mkdir firstapp

  2. cd firstapp

  3. npm init -y(-y省掉设置参数的步骤)

  4. touch index.js

  5. npm install express

  6. npm i -g nodemon (nodemon to auto-restart server)

  7. nodemon index.js
  8. 

const express = require("express")
const app = express();

app.listen(8080, () => {
    console.log("this is 8080 port")
})

app.get('/', (req, res) => {
    res.send('welcome to the home page~')
})

app.get('/cat', (req, res) => {
    res.send('meow~')

})

app.post('/han', (req, res) => {
    res.send('Lieeee')

}). //open postman, choose post setting, then sent, get Lieeee.

app.get('/dog', (req, res) => {
    res.send('woof~')
})

//set multiple parameters
app.get('/r/:subreddit/:postID', (req, res) => {
    const { subreddit, postID } = req.params;
    res.send(`<h1>Viewing Post ID: ${postID} on the ${subreddit} subreddit</h1>`)
})

//working with query strings
app.get('/search', (req, res) => {
    const { q } = req.query;
    if (!q) {
        res.send('NOTHING FOUND IF NOTHING SEARCHED!')
    } else {
        res.send(`<h1>Search results for: ${q}</h1>`)
    }
})

// if can not find matching routing
app.get('*', (req, res) => {
    res.send("I don't know the path~")
})