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22.03.14 - Javascript

Javascript is embedded in a webpage. Java is used to write desktop and enterprise apps. Boundaries are becoming more blurred

  • Interpreted Language with browser as the interpreter
  • Client-side rather than server-side. Means it runs in the users browser rather than on the webserver
  • Compatibility depends on browser version, but virtually every browser supports it
  • Security cannot access the clients system beyond their web browser, so no file access

Javascript is not OOP, does not support class-based inheritance

Javascript can change any elements in HTML document

To declare variables in JS, have to declare it using var, JS doesnt care if it is a int etc. Can mix and match variables throughout the program. Can convert int to string and string to int NaN - Not a Number

Arrays​

If added item to index 7, with only 2 elements, will fill in the gaps with undefined .push() - adds an elements to the end of the array .indexOf() - Check whether an array already contains a specific value .join() - Gives control over how the array values are concatenated together

Functions​

Variables declared in functions are local. Return value is the parameter of return

Parameters​

  • There is no type checking of parameters, nor is the number of parameters checked
  • All arguments are sent through a property array
  • Can access this array inside the function

Objects​

  • Are like variables but they can contain many values.
  • Can add new properties to an existing object simply by giving it a value.
  • Can use the delete keyword to delete a property

DOM - abstract model that defines the interface between documents and application programs - an API HTML DOM is a standard object model and programming interface for HTML. Defines:

  • Properties of all HTML elements
  • Methods to access all HTML elements
  • Events for all HTML elements

DOM have a tree like structure eb4a70e6f2c829160a46b0b9d7d8e7b2.png

Can find elements by id, tag name and class name

.getElementById .getElementsByClassName

Events and Event Handling​

  • An event is a notification that something specific has occurred
  • Is a script that is implicitly executed in response to the appearance of an event
  • The process of connecting an event handler to an event is called registration

Dynamic HTML​

HTML document whos properties can be changed after the document has been and is still being displayed by the browser

Form Validation​

  • Most popular use for JS
  • Should primarily be used for assistance for users to verify that the data inserted is in the right format. Would need to do further validation through PHP

Screen Output​

alert - Single ok button confirm - Ok and Cancel button prompt - Ok and Cancel button and input field