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Mark Down Syntax

4/4/9

Mapping Functions to HTML Elements

  • When adding a function to an html element, the function will not be added if the elements arent loaded beforehand. to fix this, use document as such:

    $(document).on('click', .className, function(){alert('hi')})

Using this with ()=>{} (DON'T DO IT)

  • When using "this" on an onclick, make sure to NOT use arrow functions. arrow functions will lift the state of the function 1 scope higher, which will return the window instead of the html elemnt

Body Parser

  • Body-parser npm package allows us to parse the 'req.body' object
  • This pertains only to POST requests. Post requests are sent through the body, not the url.

Using Post vs Get

  • Using POST will not allow the user to continuously carry out an action mapped to that route
  • POST requests are sent through the req.body object. To read this obj server side, you need body parser.
  • GET requests are sent through the url (it can be accessed from the browser), which can be bookmarked and sent to multiple users.
  • By virtue of these properties, never use GET for routes that will alter or update the DB.
  • GET should only be used to read the data

MethodOveride

  • PUT and DELETE is not built into express. This 'hard-codes' it in so we can use it.
  • POST is changed in the server.js to PUT or DELETE
  • Using ajax: url:'/actors-delete?_method=DELETE' url:'/actors-update?_method=PUT'
  • Please note that PUT and DELETE have both been built into express. This is no longer needed.

Using Forms instead of Ajax

  • Forms are used when you dont want to use javascript
  • If its a simple application, maybe extra js is not needed
  • action: URL?_method=PUT and method= POST
  • Use res.redirect('/') to allow the page to just reload

4/6/9

EJS (Embedded JS)

  • These templates allow you to mix the html and js together
  • Linking html elements from separate html file allows elements to be reused on multiple pages. Updating a file once will update on all the pages that uses it.
  • This is an alternative to making ajax calls and displaying information to the page
  • Integrating ejs into express: app.set('view engine', ejs);
  • The public folder is still needed for images and links or serving a single page up front. But use EJS
  • res.render(pages/animals',{data}) looks for a folder called views and look for a file named animals.

Sessions

  • This needs cookie-parser and express-session
  • This allows a user to stay logged in for multiple pages
  • Simlar to localStorage on the browser.
  • Syntax : res.session.na
  • Restarting the server will dump all the sessions
  • To manual dump session : req.session.destroy()

4/9/9

Sessions

  • the req.session.na object is basically an object that is global to the entire server. This allows the object to be continously read by other routes.

Prepared Statement

  • using ? in a SQL query and to keep the user from directly sending queries to the database

bcrypt.js

  • bcrypt.genSalt(10, function(err, salt)
  • creates a salt which is randomly generated characters
  • the salt is then used to encrypt the raw password together
  • bcrypt.hash(req.params.password, salt, function(err, p_hash) {

4/10/9

Sending Data w/ Form and POST

  • When sending sensitive data, make sure to use POST request instead of GET. Post will be sent through the body object but get requests will be sent through the url.
  • In the input of each data, specify a name attribute or else the information will not have a key in the object. Ex:
    • <input name="emai">

4/11/9

File Path in Browser

  • When referencing paths in the browser, the path will begin at the root of the folder. Its is not needed to find the path out of the current folder.

4/13/9

jQuery Attr

  • When accessing the attr of a jquery element, you cannot use a variable because the attr. is not a function of a newly created variable
  • For example: var allIcons = $('.allIcons'), allIcons.attr('name') will not work.
  • Instead, dont use a variable at all and just call attr. directly from the jquery element

4/21/19

Designing Data-Intensive Applications: The Big Ideas Behind Reliable, Scalable, and Maintainable Systems (Preview Edition)

  • A data-intensive application is typically built from standard building blocks which prodive commonly needed functionality. For example, many applications need to:

    • Store data so that they, or another application, can find it again later (databases)

    • Remember the result of an expensive operation, to speed up reads (caches)

    • Allow users to search data by keyword or filter it in various ways (search indexes)

    • Send a message to another process, to be handled asynchronously (stream processing)

    • Periodically crunch a large amount of accumulated data (batch processing)

    • Notes notes notes

4/25/19

Basics of MongoDB

  • Reporting is much much easier to do with MySQL. Don't use MongoDB for reporting. DONT!

  • Enterprise software would not be using a NoSQL database. There are just too many relationships.

  • If you have to WRITE lots of data, web scraping, less structure use MongoDB.

4/27/19

Cherio

  • Uses jquery on the backend to efficiently scrape data from html - Only works if the data is loaded WITH the html, not AFTER - This will work for any site before 2009

Nightmare

  • Same as Cherio but it will work on pages made with data loaded AFTER html

4/28/19

ASCII vs Unicode

  • ASCII defines 128 characters, which maps to the numbers 0-127. It uses 7-bits to define a characters.

    • Not 8 because back then, the last bit was used to avoid error as parity bits

  • Unicode defines around 2^21 characters, which maps to the numbers 2^21

  • ASCII was created with the english language in mind. Unicode has essentially all the letters of other languages defined by the Unicode numbers. This means that ASCII is a subset of Unicode.

  • Here is a great explanation of it unicode-vs-ascii

4/29/19

  • A good way to set up the database of a social network application is by using graphs. Graphs is a data structure that consists of nodes and edges, similar to trees and linked lists.

  • By using BFS, you can find the shortest path between you and another user.