Introduction to JavaScript I

• Run
• Declare
• Variables vs constants
• Primitives*6
  string, number, boolean, undefined, null, symbol
• References*3
  object, array, function
• Basics of array, string, function

// run: in browser or node
console.log("hello world!"); 
// node index.js // run in node

// variable
// use let to declare a variable
let name //undefined
name = "Chandler"; 
 console.log(name);

// constants, don't need to assign
const interestRate = 0.3; 
// interestRate = 1;
console.log(interestRate);

// primitive/value types * 6
// string, number, boolean, undefined, null, symbol. primitive types don't have properties and methods, only object types do.
let firstName = "Monica";
let age = 30; // don't have float numbers or integers, all are number type
let isApproved = true;
let lastName; // undefined
let middleName = null; // type: object

// dynamic typing
// type of variable can be changed.


/* // refrence types * 3
// object, array, function */

//object
let person = {
    name: 'Ross', // property
    age: 10
};
// dot notation
person.name = "Rachel";
// bracket notation
person["name"] = "Emma";
let selection = "name";
person[selection] = "Pheabe";
console.log(person)

// arrays
let selectColors = ['red','blue']; // type: object
selectColors[2] = 'green';
selectColors[3] = 20;
console.log(selectColors);
console.log(selectColors.length);
console.log(typeof(selectColors));

// functions
// function is a set of statements that either performs a task or calculate and returns a value.
function greet(firstName,lastName){ // name: parameter
    console.log('Hello ' + firstName + ' ' + lastName);

} // do not need to terminate with ;
greet('Joey'); // argument
greet('Chandler','Bing');

// calculating a value
function square(number){
    return number*number;
}
let number = square(2);
console.log(number);


// string primitive
const message = 'hi';
console.log(typeof message)
// string object
const another = new String('hello');
console.log(typeof another)

Thanks for @Mosh‘s great video tutorials.