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57 lines
1.5 KiB
Markdown
57 lines
1.5 KiB
Markdown
---
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title: "javascript"
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aliases:
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tags:
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- cosc203
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---
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An dynamically typed interpreted scripting language to dynamically control websites.
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# HTML DOM
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(Document object model)
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- JS can access and alter [html](notes/html.md) elements
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- When a page loads it creates the DOM as a tree of objects
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# Using js
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Add inline, external or internal (script tags) js
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loading
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- defer makes scripts run only after all scripts are loaded
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- async scripts run as soon as they are loaded (no order guaranteed)
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# Events
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Triggered by various things that happen on a webpage
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You can add an event listener to an element, which will trigger a function when that event occurs
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# Cookies
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Used to store data on client machines
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Allows server to "remember users"
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# Limitations
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- Cannot access client files
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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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- no multithreading
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- cannot read history
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- cannot open invisible windows
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# Async
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Allows running long tasks in background while browser remains responsive
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process
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- Call function - returns a promise immediately
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- When function is finished - we are notified and promise become a value
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callback: function passed to another function
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promise: object which represents the status of a function
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- pending
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- fulfilled -> .then
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- rejected -> .catch
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- settled (fulfilled or rejected)
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await: keyword within as async function which makes code wait at a point for a task to finish
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## Fetch
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Used to request data from a server to update the page. |