quartz/content/notes/05-javascript.md

title	aliases	tags	sr-due	sr-interval	sr-ease
05-javascript		lecture cosc203	2022-08-06	8	250

Javascript

DOM

• JS can access and change all the elements of an HTML document
• When a webpage is loaded, the browser creates a DOM of the page
• The HTML DOM model is contructed as a tree of Objects

JS can:

• change elements
• change attributes
• change styles
• remove elements
• add new elements
• react to events
• create new events

JS is

• descriptive
• structued
• interpreted

can be linked externally

• <scipt src="script.js" defer></script>
• defer ensures that the js is loaded after the html (in a specific order)
• async ensures that the js is run as soon as it is loaded (not in a specific order)

typing

• js is dynamically typed
• you dont need to specify the type of variable

events

• e.g., click, hover, resize etc
• smoke alarm analogy
  • fire is the event
  • alarm is the listener
  • sound of the alarm is the handler

cookies

• websites can use JS to store cookies on client machines.
• usually server 'serve' the file to the user and nothing else
• cookies allow to server to remember information about the client
• document.cookie

limitations

• cannot write to files (apart from cookies)
• cannot execute programs on client computer
• cannot establish a connection to any server except the one it came from (apart from re-directing to a new site)
• cannot read history of brower (but is can cause the brower to move around in the history list)
• not supposed to be able to open an invisible window