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62 lines
1.6 KiB
Markdown
62 lines
1.6 KiB
Markdown
---
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title: "05-javascript"
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aliases:
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tags:
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- lecture
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- cosc203
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sr-due: 2022-07-29
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sr-interval: 3
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sr-ease: 250
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---
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# Javascript
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## DOM
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- JS can access and change all the elements of an HTML document
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- When a webpage is loaded, the browser creates a DOM of the page
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- The HTML DOM model is contructed as a tree of Objects
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JS can:
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- change elements
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- change attributes
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- change styles
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- remove elements
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- add new elements
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- react to events
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- create new events
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JS is
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- descriptive
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- structued
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- interpreted
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can be linked externally
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- `<scipt src="script.js" defer></script>`
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- `defer` ensures that the js is loaded after the html (in a specific order)
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- `async` ensures that the js is run as soon as it is loaded (not in a specific order)
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typing
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- js is dynamically typed
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- you dont need to specify the type of variable
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events
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- e.g., click, hover, resize etc
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- smoke alarm analogy
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- fire is the event
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- alarm is the listener
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- sound of the alarm is the handler
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cookies
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- websites can use JS to store cookies on client machines.
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- usually server 'serve' the file to the user and nothing else
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- cookies allow to server to remember information about the client
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- `document.cookie`
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limitations
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- cannot write to files (apart from cookies)
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- cannot execute programs on client computer
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- cannot establish a connection to any server except the one it came from (apart from re-directing to a new site)
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- cannot read history of brower (but is can cause the brower to move around in the history list)
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- not supposed to be able to open an invisible window
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