JS_notes.md

JavaScript Basics

• ECMAScript standards, it stands for the European Computer Manufacturers Association (ECMA). Which gives standards to JS.

• Variables

  Primitives are single self related like numbers, boolean, strings etc Compounds data are held as arrays objects

• We use let and const to declare variables

• Arrays

const arr = [1,2,3] console.log(arr[0])

• Objects (also known dictionaries in other languages)

const obj = {
  name: "Siat",
  email: "siat@ymail.com"
}
console.log(obj.name)

DOM (Document object model)

• It's the JS representation of the structure of HTML and is present in the variable document when we load the page

 document 
 {} like querySelector() 
 element
 {} {} {} like .addEventListener().style.color

• All this is possible with the set of methods called the Browser API

Other

• Its a C like language, meaning it's most of the syntax came from C
• It contains if, while, for and more

Loop

• we use for in loop to iterate object example

const obj = {
  name: "siat",
  age: 26
}
for(let key in obj) {
  console.log(key.obj[key]);
}

Sample Output: 'name' 'siat' 'age' 26

• we use for of to iterate array

let nums = [1,2,3,4]
for(let num of nums) {
  console.log(num)
}

Sample output: 1 2 3 4

Functions

• we declare functions by special keyword function after that name add and inside that we need to put the parameter

function add (first, second){
  return first+second;
}
add(1,2) // declare the function or use the function 
// here 1 2 are the arguments

Methods

• methods are same as functions
• that they are attached to different data types

"hi" .toUpperCase() // HI
['c', 'b', 'a'] .sort()    // ['a', 'b', 'c']
[1,2,3] .indefOf(1) // 0

Arrow Function

• function can be written like this
• now a days arrow functions are used most

Async Programming

• we can say it's like performing non-deterministic operation
• Some important parts
  • Network Request to server

    fetch(http:://server)

  • Callbacks, promises

Async Await

Typescript

• It compiles into normal javascript
• It gives static variable
• we need to mention variable type in TS

NPM

• Node Package Manager
• We can use various packages with npm