class-6 Javascript "this" and first class function

//javascript 'this', call bind apply

//"this"
//global execution context
//functional execution context

// const a = 10

// function sum(num1, num2) {
//   return num1 + num2
// }

// console.log(sum(10, 15))
// console.log(a)

//in global execution context - window
// In functional execution context
//- plain function call - window, undefined(in strict mode)
//- with object chaining- that object
// inside constructor function - empty object
//in strict mode (plain function call) - undefined

// console.log(this) // window

// function greet() {
//   console.log(this) //window
//   return 'Hi'
// }
// //how you call the function
// //plain way - window
// greet()

// const person = {
//   firstName: 'samim',
//   lastName: 'Fazlu',
//   fullName() {
//     console.log(this)
//     // const $that = this

//     // function inner() {
//     //   console.log($that)
//     //   return $that.firstName + ' ' + $that.lastName
//     // }
//     //arrow function has no this binding
//     const inner = () => {
//       return this.firstName + ' ' + this.lastName
//     }
//     console.log(inner())
//   },
// }

// person.fullName()
// const fullName = person.fullName
// console.log(fullName.call(person))

// function Person(){
//     //this = {}

//  this.fName = 'samim'
//  console.log(this)
// }

// const samim = new Person()
// console.log(samim)

// function greet(lName, age) {
//   return 'Hi' + ' ' + this.name + ' ' + lName + '-' + age
// }
// //you can define 'this'
// const person = { name: 'samim' }
// // const obj = greet.call(person, 'Hasan', 30)
// // const obj = greet.apply(person, ['Hasan', 30])
// //work like call , function is not called
// const boundFunc = greet.bind(person, 'Hasan', 30)
// //this can't be changed (after bind once)
// console.log(boundFunc())

//first class function

//function(value) can be used as any data type

//functions can be assigned to any other variable or passed as an argument or can be returned by another function

// A “higher-order function” is a function that accepts functions as parameters and/or returns a function.
//greet -higher order function
//func - callback function
// const greet = (fn) => {
//    fn('Hi')
//   //   console.log('Hi')
// }

// const func = function (initial) {
//     console.log(initial + ' ' + 'world')
//   }

// console.log(
//   greet(func)
// )

//Higher order function
//lambda function (innerFunc)
function sum(num1) {
  return (num2) => {
    return num1 + num2
  }
}

// const secondFunc = sum(3)
// console.log(secondFunc)
// console.log(secondFunc(2) )
// console.log(sum(3)(2))