express use() code example

Example 1: app.get

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

const { getElementById, getIndexById, updateElement,
  seedElements, createElement } = require('./utils');

const PORT = process.env.PORT || 4001;
// Use static server to serve the Express Yourself Website
app.use(express.static('public'));

const expressions = [];
seedElements(expressions, 'expressions');
const animals = [];
seedElements(animals, 'animals');

// Get all expressions
app.get('/expressions', (req, res, next) => {
  res.send(expressions);
});

// Get a single expression
app.get('/expressions/:id', (req, res, next) => {
  const foundExpression = getElementById(req.params.id, expressions);
  if (foundExpression) {
    res.send(foundExpression);
  } else {
    res.status(404).send();
  }
});

// Update an expression
app.put('/expressions/:id', (req, res, next) => {
  const expressionIndex = getIndexById(req.params.id, expressions);
  if (expressionIndex !== -1) {
    updateElement(req.params.id, req.query, expressions);
    res.send(expressions[expressionIndex]);
  } else {
    res.status(404).send();
  }
});

// Create an expression
app.post('/expressions', (req, res, next) => {
  const receivedExpression = createElement('expressions', req.query);
  if (receivedExpression) {
    expressions.push(receivedExpression);
    res.status(201).send(receivedExpression);
  } else {
    res.status(400).send();
  }
});

// Delete an expression
app.delete('/expressions/:id', (req, res, next) => {
  const expressionIndex = getIndexById(req.params.id, expressions);
  if (expressionIndex !== -1) {
    expressions.splice(expressionIndex, 1);
    res.status(204).send();
  } else {
    res.status(404).send();
  }
});

// Get all animals
app.get('/animals', (req, res, next) => {
  res.send(animals);
});

// Get a single animal
app.get('/animals/:id', (req, res, next) => {
  const animal = getElementById(req.params.id, animals);
  if (animal) {
    res.send(animal);
  } else {
    res.status(404).send();
  }
});

// Create an animal
app.post('/animals', (req, res, next) => {
  const receivedAnimal = createElement('animals', req.query);
  if (receivedAnimal) {
    animals.push(receivedAnimal);
    res.status(201).send(receivedAnimal);
  } else {
    res.status(400).send();
  }
});

// Update an animal
app.put('/animals/:id', (req, res, next) => {
  const animalIndex = getIndexById(req.params.id, animals);
  if (animalIndex !== -1) {
    updateElement(req.params.id, req.query, animals);
    res.send(animals[animalIndex]);
  } else {
    res.status(404).send();
  }
});

// Delete a single animal
app.delete('/animals/:id', (req, res, next) => {
  const animalIndex = getIndexById(req.params.id, animals);
  if (animalIndex !== -1) {
    animals.splice(animalIndex, 1);
    res.status(204).send();
  } else {
    res.status(404).send();
  }
});

app.listen(PORT, () => {
  console.log(`Server is listening on ${PORT}`);
});

Example 2: what is app.use() used for

//app.get will see only exact match ex.> "/book" here app.get will not allow /book/1, etc 
//but app.use is different see below

//what is difference between app.use and app.all
//app.use takes only 1 callback while app.all takes multiple callbacks
//app.use will only see whether url starts with specified path But, app.all() will match the complete path

app.use( "/book" , middleware);
// will match /book
// will match /book/author
// will match /book/subject

app.all( "/book" , handler);
// will match /book
// won't match /book/author   
// won't match /book/subject    

app.all( "/book/*" , handler);
// won't match /book        
// will match /book/author
// will match /book/subject

Example 3: express mounting router

app.get(/a/, function (req, res) {
  res.send('/a/')
})