2023-04-27

This is Maëlle's DBGI daily open-notebook.

Today is 2023.04.27

TODO

Check discussion: https://github.com/orgs/digital-botanical-gardens-initiative/discussions
Check Zulip

CODE

NOTES

JS tutorials

https://www.youtube.com/playlist?list=PL4cUxeGkcC9haFPT7J25Q9GRB_ZkFrQAc

variable creation

let => can be changed
const => can't be changed
var => older way

variable comparison

== equals
!= not equals
=== equals and same type
!== not equals to type
&& and
|| or
!boolean inverse
Check type => typeof variableName

Loops

for(let i=0,i<5,i++){}
while(i<5){}
do{}while(i<5) => run the 'do' code one time before checking for condition
if(){} else if{} else{}
When testing multiple elif on same variable =>

switch(variableToTest){ 
  case 'A':
    code;
    break;
  case 'B':
    code;
    break;
  case 'C':
    code;
    break;
  default:
    code;
    }

functions

function declaration:

function name(){
  code;
  return ...;
}

call function: name();

function expresion:

const variable = function(){
  code;
  return ...;
};

call expression: variable();

function declaration is happening at the beginning of the script even if it is defined at the end whereas function expression not.

arrow function:

const variable = (arguments) => code;

method

functions that are called as '.method' after an object

callbacks

functions that are used in another function as argument

object.forEach(function(){
  console.log('something');
})

or with arrow function:

object.forEach(()=>{
  console.log('something');
});

Objects

= python class

let user = {
  name: 'crystal',
  age: 30,
  email: 'crystal@thenetningja.co.uk',
  location: 'berlin',
  blogs: [
          {title: 'blog1',likes: 30 },
          {title: 'blog2', likes: 20}
          ],
  login: function(){ // method creation
    console.log('the user logged in')
  },
  logBlogs(){
    this.blogs.title // 'this' calls the object
  }
};

// access value
name = user.name; 
name = user['name'];

// change value
user.age = 35; 
user['age'] = 35;

// call method
user.login()

Node.js tutorials

https://www.youtube.com/playlist?list=PL4cUxeGkcC9jsz4LDYc6kv3ymONOKxwBU

Introduction

Node.js permits to read and write files on a computer
connect to a database
Act as a Server for content
no need to link to html files

=> Role is to run JS on the backend

Why use Node.js?

share code between front and back en as they use both JS
Huge community behind it
Huge amouont of third-party packages and tools to help

streams and buffer

When loading data => not all at once but more like a stream.
Load data in buffer => when buffer is full => pass data

const readStream = fs.createReadStream('./docs');

readStream.on('data',(chunk) => {
  code
});

Chunk is passed when buffer is full

Can do the same for writing files with fs.createWriteStream().

piping

read a file and write readStream.pipe(writeStream);

TODO NEXT

Continue node.js course from #7