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https://github.com/suyashsingh/expressjs

Express Sample Codes
https://github.com/suyashsingh/expressjs

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Express Sample Codes

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README 

        
# expressjs

Express Sample Codes



## Basics:



* Express is a Node.js web application framework.



* Express is used to make:



 1. Websites

 2. Web apps

 3. Back Ends



* Pug(earlier known as jade) is used to creating HTML templates.



* Competetors: Rails, Django



* Developed by TJ *Holowaychuk*, maintained by Node.js foundation.



* npm is the package manager for node.



* Packages can be installed using `npm install` command. The installation can be

    of two types, either *local* or  *global*. In local installation the packages

    will be available only with in the directory. While packages in global can be

    acessed throughout the system.



    `npm install -g name_of_package` is the systax for global installation.

    

    For local installation omit the `-g` flag.



* `npm init` is used for creating `package.json` file. This file is used to list down

    the dependencies. So it is good if you generate this file.



* Simple Hello world application



    var express = require('express');

    var app = express();



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

    res.send("Hello world!");

    });



    app.listen(3000);



    

    `app.get(route, callback)`. the `get` can be replaced by any of the HTTP requests.

    The callback function will be called when the client requests that url.



    The callback function has two parameters, request(req) & response(res).



* The HTTP requests are also called `HTTP verbs` at places.



* `route` is an *endpoint* in the url. eg. www.example.com/hello here `/hello` is a route.



* You can have multiple callback methods at the same route. e.g you can have app.get("/", ...), 

app.put("/", ...),  app.get("/", ...), etc.



* You can also use the *all* method to handle all HTTP requests using a single method. This is

benifitial in defining middle wares.



The syntax is: 



    app.all('/hello', function(req, res){

    res.send("This method will handle all the requests.");

    });



*Routers: Using routers will make the code more maintainable as the routes are defined in separate file.



* Routes can be either static or dynamic.



* Passing parameters in the url will be an example of `Dynamic route`. Dynamic routes can be used

    at any level you want. For eg. at root level or at a sub level, say at `/hello`.



* You can match patterns in your route, and the requests that escape the pattern can be matched using the `*`

    wild card in the route. 

    *As express processes the main js file i.e. either app.js or index.js from start to end.*

    *Put the match every thing pattern at the end*



## Examples



Express Hello-World Example: myapp

---

* Use the `npm init` command to add package.json file.

* Install *express* using `npm install express`.



Express Generator Hello-World Example: genapp

---

Install the `express-generator` package using: `npm install express-generator -g`



But this will install express-generator globally as you have selected the *global install* options `-g`.



Genreate the app with pug as the view engine. If you want to change the view engine and see other options: `express -h`

`express --view=pug genapp`



`npm start` To start the application.



Open the page `localhost:3000`



Routing

---

Routing simply means what action will be taken when there is a client request on a particular URL & 

a specific HTTP request method.



The key points are:



1. URL



2. [HTTP Request Method](https://en.wikipedia.org/wiki/Hypertext_Transfer_Protocol#Request_methods) (GET, POST, PUT, DELETE, HEAD, OPTIONS)



   

You can use [Postman](https://www.getpostman.com/apps) to send HTTP requests you want.