variable

before ES6 we use the var keyword.

let name = 'Amy';

console.log(name);

//varable name cannot be a reserved key word

//should be meaningful

//cannot start with a number(1name)

//cannot contain a space or hyphen(-)

//are case-sensitive

let firstName;

let lastName;

constant

const interestRate = 0.3;

primitive/value types: String, Number, Boolean, undefined, null

reference types: Object, Array, Function

typeof name

Dynamic typing

Objects

curly braces

let person = {

name: 'Nosh',

age: 30

};

//Dot notation

person.name = 'james';

//bracket notation

person['name']='mary';

Array

let selectedColors = ['red', 'blue'];
selectedColors[2] = 'green';
console.log(selectedColors[0]);

Tycinically, array is object too.

Functions

function greet(){

  condole.log('hello word');
}
greet();

function greet(name){

  console.log('hello'+name);
}
 
greet('John');

//calculating a value
function square(number){
  return number * number;
}

let number = sqaure(2);
console.log(number);