JavaScript Essentials

JavaScript

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Terms in this set (97)

A scripting programming language of the web, invented for the web, run client side by web browsers, that adds interactivity to a web page. JavaScript is a language that works with and manipulates web pages. It only works within web browser applications that have a JavaScript engines. Code is sent to the client and is interpreted there. Does not run server side.

What can JavaScript do?

- Create an active user interface.
- Tailor the user experience(more personal), different content based upon the day, time, browser etc.
- Extend the user experience such as dynamic pages, user interface elements that react to user input.
- Validate user input on forms such as pre processing forms.
- Create custom HTML pages on the fly
- Control Web browsers

What can't JavaScript do?

- Talk to a database
- Write to files
- Keep a counter
- Keep track of state (except with cookies)
- Access local files or hardware

Execution Order

Starts at the first statement and moves down. JavaScript is parsed and interpreted as soon as its hit by the browser. And that means your JavaScript file could cause a delay in rendering the page. We don't want to slow the page down.

DOM simplified

Document - The web page
Object - The pieces of that web pages
Model - The agreed-upon set of terms

DOM

A language / interface that allows programs and scripts to dynamically access and update the content, structure and style of documents. The DOM is a family-tree structure of sorts. HTML like other markup languages uses this model to describe the relationships of things on a page. When we refer to these relationships, we use the same terminology that we use to refer to family relationships - parents, children, etc. The document is the webpage. The object that handles the contents of a webpage is the document object.Objects are for example (window, location, history, navigator, document). Model is a way of thinking about things in the browser. A model is a representation of something and in this case the document.

DOM Scripting

DOM scripting is the process of building a web application by using JavaScript to manipulate the DOM. DOM scripting uses event driven programming. event = action performed by the user. event handler = javascript code executed to process the event.

Object

The elements / the components on the page that sometimes contain other objects. Objects are collections of name/value pairs having a hidden link to a prototype object. Every object has a property (variable belonging to an object.) and a method (a function that the object can invoke).

Model

M in DOM stands for Model which is a representation of the webpage. You can use Javascript to read this map. In order to gain information from the model, you need to understand what conventions are being used to represent the document (node (point of connection) tree)

Variables

Its a container that we create, name, and give a value. Values subject to change. Giving a value to a variable is called assignment. var thePage; Variable names cant start with number, dashes or spaces. Must be written as one word and no spaces. You can declare a variable and set it at the same time. var myCat ="Pixel"; Any variable can contain most anything (numbers, strings,booleans)