02. Javascript Scope Lesson

/*****************************************Higher Order Functions************************************ */

// 1.Assigning Functions to Variables

// const square = function(x) {
//   return x * x;
// };
// console.log(square(5));

// const foo = square;
// console.log(foo(6));

// 2.Passing Functions as Parameters

// function sayHello() {
//   return "Hello, ";
// }
// function greeting(fn, name) {
//  console.log(fn() + name);
// }

// greeting(sayHello, "JavaScript!");


// 3. Return a function

// function sayHello() {
//   var a = "Hello"
//   return function() {
//     console.log(a);
//   };
// }
// console.log(sayHello()());

// Global
// Local
// Block
// Lexical



/************************************** Variables ***************************************************** */

// Variable - Var

// console.log(greeter);
// var greeter = "say hello";
// var greeter = "hello again";
// console.log(greeter);

// Weakness of var

// var greeter = "hey hi";
// var times = 4;

// if (times > 3) {
//     var greeter = "say Hello instead";
// }

// console.log(greeter)

// Varibale - LET

//1. let is block scoped

// let greeting = "say Hi";
// let times = 4;

// if (times > 3) {
//      let hello = "say Hello instead";
//      console.log(hello);//"say Hello instead"
//  }
// console.log(hello) // hello is not defined

//2. let can be updated but not re-declared.

// let greeting = "say Hi";
// let greeting = "say Hello instead";
// console.log(greeting)

// Varibale - CONST

// 1.const declarations are block scoped

// 2. const cannot be updated or re-declared

// Differences

// 1. var declarations are globally scoped or function scoped while let and const are block scoped.

// 2. var variables can be updated and re-declared within its scope;
// let variables can be updated but not re-declared;
// const variables can neither be updated nor re-declared.

// 3. They are all hoisted to the top of their scope but while varvariables are initialized with undefined, let and const variables are not initialized.

// 4. While var and let can be declared without being initialized, const must be initialized during declaration.

// var a;
// a = 10;
// let b;
// b = 20;
// const c = 44;
// console.log(b)


// ************************ Conditions ***********************************/

// Ternary Operator

// let age = 80;
// let message = age > 18 ? true : false;
// console.log(message)

// Ternaray Opearator - Multiple Conditions
//  let age = 80;
// let message;
// if (age < 3) {
//   message = 'Hi, baby!';
// } else if (age < 18) {
//   message = 'Hello!';
// } else if (age < 100) {
//   message = 'Greetings!';
// } else {
//   message = 'What an unusual age!';
// }
// console.log(message)

// let message = (age < 3) ? 'Hi, baby!' :
//   (age < 18) ? 'Hello!' :
//   (age < 100) ? 'Greetings!' :
//   'What an unusual age!';

//  console.log(message)

// undefined, null, 0, "", NaN

// Short Circuit Evaluation


// if (-1 && 0) {
//   console.log("daf");
// }

// var a = 11;
// var n = a && 4 && 10 && 6;
// console.log(n)


// let a = 2 + 2;

// switch (a) {
//   case 3:
//     console.log('Too small')
//     break;
//   case 4:
//     console.log('Exactly')
//     break;
//   case 5:
//     console.log('Too large')
//     break;
//   default:
//     console.log("I don't know such values")
// }