WebFund 2015W Lecture 3
Audio and video from the lecture given on January 12, 2015 are now available. The video has a partial audio track due to corruption; for full audio listen to the mp3.
Notes
Web applications versus web pages *Web page HTML + CSS + JAVASCRIPT
HTML(Hyper Text Mark Up Language) defines structure of page (define HTML) CSS is responsible for the styling of the webpages JavaScript is the code of the webpage
Web Applications:Set of webpages + Server side logic
when you a loading a webpage the serves does two things: 1)browser sends HTTP GET 2) Server returns HTML document * The document has references to other resources _ The browser does GETs for those
What does the server side logic do?
1) It changes what is returned in response to GETs, (and POST)
Static Web Servers serve files, while on the other hand Dynamic web servers implement logic.
Early web server used CGI to do dynamic web pages
CGI: Common Gateway interface An Example of a CGI would be a program, for example a perl script
the web started with static web pages
The problem with using CGI for everything is that: 1) You have to run seperate process for each web request, which is rather expensive and not a great architecture
One solution is to keep dynamic program running -this is usually used with PHP because a new process does not have to be spawn each time.
Keep in mind that node does not eliminate a static server, but instead it offers an easier way to implement
a dynamic server .
What is node? Node is a javascript execution environemnt with networking and disk Input and Ouput(I/O) support
Javascript is limited in what it can do
On the other hand, node by itself does not have much functionality, we need to add *modules* to make it better
NPM = node package manager
The node package manager lets us load the modules that a node application depends on.
FrameWork: All a framework is a scaffolding for an application
Also a framework helps you to gennerate a simple application that runs but doesnt does much, then you have the functionality you want.
app.js: contains the code Public folder : anything you put in here, static web server i.e images, style sheets etc
keep in mind this folder is not the only folder that contains, but also this is where the highest
level configuration of web application also takes place.
packages.json: contains dependencies bin: contains the file you run
with node,all the code you will need will live in a node_module directory we type cat package.json on the terminal to view the dependencies
we also type "npm install" on terminal to install the NPM after the instalation is complete a node module directory will be downnloaded/installed
now we can run the web server.
localhost:3000? what does this mean
localhost is the machine you are operating on. In 2406 we will do everything off localhost. local host can be replace with your ip i.e 134.117.222.90:3000 3000 is the default
3000 is the standard development port we will be using.
usually to connect to port 80 you have to priviledges, and we do not want that, because no one knows how your code will react.
favicon is the little icon that shows on the corner of your browser while it is running.
JavaScript -it is loosely type -Weird globals -null is an object etc
JavaScript can also be said that it can be said that it is a first draft of a great language.
First rule of the web is Compatibility , and which is one of the reasons why JavaScript has not "fixed"
Properties of JavaScript -C like syntax -loosely typed : what does this mean? It means you do not specify types for variables, that doesn't mean there are no types -identifiers can refer to data of any type -numbers are ALL DOUBLES i.e Double Precision Floats(floating point i.e no integers) -Object Oriented -NO CLASSES - only prototypes -lexical scoped: meaning the range of which a variable can be seen or range of functionality of a variable, so that it can only be called from the scope/ the block of code where the variable was defined
Prototypes have no compile phase. JavaScript also has no compile phase.