quartz/content/notes/javascript.md

title	aliases	tags
javascript		cosc203

An dynamically typed interpreted scripting language to dynamically control websites.

HTML DOM

(Document object model)

• JS can access and alter html elements
• When a page loads it creates the DOM as a tree of objects

Using js

Add inline, external or internal (script tags) js

loading

• defer makes scripts run only after all scripts are loaded
• async scripts run as soon as they are loaded (no order guaranteed)

Events

Triggered by various things that happen on a webpage

You can add an event listener to an element, which will trigger a function when that event occurs

Cookies

Used to store data on client machines

Allows server to "remember users"

Limitations

• Cannot access client files
• Cannot establish a connection to any server except the one it came from (apart from re-directing to a new site)
• no multithreading
• cannot read history
• cannot open invisible windows

Async

Allows running long tasks in background while browser remains responsive

process

• Call function - returns a promise immediately
• When function is finished - we are notified and promise become a value

callback: function passed to another function

promise: object which represents the status of a function

• pending
• fulfilled -> .then
• rejected -> .catch
• settled (fulfilled or rejected)

await: keyword within as async function which makes code wait at a point for a task to finish

Fetch

Used to request data from a server to update the page.