javascript-higher-order-functions.js

// Review Terms:
    // Built in methods - premade functions made by javascript developers that are easy to invoke

    // Syntactical Sugar - a piece of code created to make a language sweeter

    // Iteration - repeating a process until a condition is met

// Higher Order Functions (HOF) - function that takes a function as an arguement

    // HOF are only called on arrays
    // Less code
    // Uses less CPU

// ForEach - great for doing something to each element in an array

    // Anonymous function - a function that is not defined or set to a variable () => {}

// [3, 4, 5, 6].forEach(() => {})

// HOF require an arguement
    // Required arguement:
        // value - current value in iteration process (array[i])
    // Optional arguements:
        // index - current index in iteration process (i)
        // array - pass the array the higher order function is called on

// [3, 4, 5, 6].forEach(value => {
//   console.log(value)
// })

[3, 4, 5, 6].forEach((value, index, array) => {
  console.log("value", value)
  console.log("index", index)
  console.log("array", array)
})

// [3, 4, 5, 6].forEach((banana, apple, orange) => {
//   console.log("banana", banana)
//   console.log("apple", apple)
//   console.log("orange", orange)
// })


// Map - iterates over each element in an array and returns a new array with the same length
    // map is great for modifying or displaying each item

const myArray = [3, 4, 5, 6]

// const mappedArray = myArray.map(value => {
//   return value * 2
// })

const mappedArray = myArray.map(currentValue => currentValue * 2)

console.log(mappedArray)
console.log(myArray)


// Expected output: ["odd", "even", "odd", "even"]

const evenOrOdd = (array) => {
  return array.map(value => {
    if(value % 2 === 0) {
      return "even"
    } else if(value % 2 !== 0) {
      return "odd"
    } else {
      return "Ooops, something went wrong here"
    }
  })
}

console.log(evenOrOdd(myArray)) // [ 'odd', 'even', 'odd', 'even' ]

// Filter - iterates over an array and narrows down what is returned based on a condition

      // Filter has a built in IF statement
      // Returns a subset of the array

const myNewArray = [7, 8, 9, 10]

// let myFilteredArray = myNewArray.filter(value => value % 2 !== 0)

let myFilteredArray = myNewArray.filter(value => {
  return value % 2 !== 0
})

console.log(myFilteredArray) // [ 7, 9 ]



// Create the code that acts on an array of mixed data and returns only the give data type based on user input

const mixedData = [3, "hi", true, 50, 4, null, "Foxtrot"]
// pass in data type we are looking for
// Input data type: "string"
// Output: ["hi", "Foxtrot"]

// Pseudocode 
// Create a function that takes in an array of mixedData and also a data type we are looking for
  // 2 parameters - array, dataType
  // make a decision about every item in the array using filter
    // return values that are equal to datatype using typeof

const showMyData = (array, dataType) => {
  return array.filter(value => {
    return typeof value === dataType
  })
}

console.log(showMyData(mixedData, "string")) // [ 'hi', 'Foxtrot' ]
console.log(showMyData(mixedData, "number")) // [ 3, 50, 4 ]
console.log(showMyData(mixedData, "boolean")) // [ true ]