Node.js Express学习笔记

Building RESTful API’s Using Express

RESTful Services

REST: Representational State Transfer

CURD operations: Create, Read, Update, Delete
HTTP Methods: GET, POST, PUT, DELETE

Express intro

Code without express:

const http = require('http');

const server = http.createSever((req, res) => {
  if (req.url === '/') {
    res.write('hello World');
    res.end();
  }
  if (req.url === '/api/courses') {
    res.write(JSON.stringify([1,2,3]));
    res.end();
  }
});

server.listen(3000);

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

app.get('/', (req, res) => { // define a route
  res.send('Hello World')
})
app.get('/api/courses', (req, res) => { // define another route
  res.send([1,2,3]);
});
app.listen(3000, () => consle.log('listening on 3000'))
app.post()
app.put()
app.delete()

Nodemon

Node monitor, a tool that restarts our program when changes happen.

Environment Variable

const port = process.env.PORT || 3000;
app.listen(port, () =>console.log(`listening on port ${port}...`));

Route Parameters

app.get('/api/courses/:id/:month', (req, res) => { 
// :xx is the request params, we also have query parameters
  res.send(req.paras.id);
  res.send(req.paras.quert);
});

Handling HTTP GET & POST requests

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

app.use(express.json()); //a piece of middleware
const courses = [
  { id: 1, name: 'course1' }
  { id: 2, name: 'course2' }
  { id: 3, name: 'course3' }
];

app.get('/', (req, res) => { // define a route
  res.send('Hello World')
})
app.get('/api/courses', (req, res) => { // define another route
  res.send(courses);
});
app.get('/api/courses/:id', (req, res) => { 
  const course = courses.find( c => c.id === parseInt(req.params.id);
  if (!course) res.status(404).send('course not found')// 404, means not found
  else res.send(course);
});

//Handling POST request
app.post('/api/courses', (req, res) => { 
  const course = {
    id: courses.length + 1,
    name: req.body.name
  }
  courses.push(course);
  res.send(course);
});

const port = process.env.PORT || 3000;
app.listen(port, () =>console.log(`listening on port ${port}...`));

We can use Postman to test the endpoint.

Input Validation (use joi package)

待填。。。

Express ( Advanced Topics)

Middleware function

eg. Route handler, take request, return a response, or pass to other middleware function
request processing pipeline.

app.use(express.json());
App.use(function(req,res, next) {
    consle.log(‘Logging…’);
    next();
}

Build-in Middleware

app.use(express.json());
app.use(express.urlencoded()); //key=value&key=value
app.use(express.static('public'));

Third-party Middleware

helmet
morgan

Environment

develop environment? or production environment. We need to know what environment we are working on. We will enable or disable certain features.

process.env.NODE_ENV //undefined
app.get('env');

Configuration

rc config package

Debugging

const xxx = requir('debug')('name of the dbfunction')
 export DEBUG=…

Templating Engines

return html markup to the client
Templating Engines: pug Mustache EJS …

app.set('view engine', 'pug')
app.set('views','./view') //default
app.get('/', (req, res) => {
  res.render('index', {title: 'My Express App', message: 'Hello'};
}
)

file: index.pug

html 
  head
    title = title
  body
    h1= message

Database Integration

Authentication

Asynchronous javaScript

eg. setTimeout(). schedule a mission in the future

Patterns for Dealing with Asynchronous Code

When asynchronous haven’t finished, we can not get access to it in the mean program, so how could we deal with it?
Three patterns: Callbacks, Promises, Async/await

Callbacks

callback is a function, we call when the result of asynchronous operation is ready.

It may cause “callback hell”, we can name the functions to rescue it.

Promise

Promise: an object that holds the eventual result of an asynchronous operation.
States :pending -> fulfilled(resolved) /rejected

const p = new Promise((resolve,reject) => {
  //kick off some async work
  //...
  resolve(1);
  //reject(new Error('message'));
})

p
  .then(result => console.log())
  .catch(err => console.log(err.message))

replace callback to promise

creating settled promises

const p  = Promise.resolve( { id:1 })
p.then(result => ......)

Parallel Promises

const p1 = new Promise((resolve) => {
  setTimeout(() => {
    console.log('Async operation 1...');
    resolve(1);
  },2000)
});

const p2 = new Promise((resolve) => {
  setTimeout(() => {
    console.log('Async operation 2...');
    resolve(1);
  },2000)
});

Promise.all([p1,p2])      // Promise.race()
  .then(result => ......)
  .catch();

Async and Await

Keyword async and await can write asynchronous code in a simple form like synchronous. And need be wrapped with try catch.

async function displayCommits() {
  try {
    const user = await getUser(1);
    const repos = await getReponsitories(user.gitHubUsername);
    const commits = await getCommits(repos[0]);
    console.log(commits);
  }
  catch(err) {
    console.log('Error', err.message);
  }
}
displayCommits();