JS篇 - Array Map() Exercises

Today, I am going to use the built-in .map() method on arrays to solve all of these problems

These assignments are from https://coursework.vschool.io/array-map-exercises/.

map() method documents: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map

1) Make an array of numbers that are doubles of the first array.

function doubleNumbers(arr){
  // your code here
}

console.log(doubleNumbers([2, 5, 100])); // [4, 10, 200]

Answer:

function doubleNumbers(arr){
  let doubleArr = arr.map(x=>x*2);
  return doubleArr;
}

console.log(doubleNumbers([2, 5, 100]))

2) Take an array of numbers and make them strings

function stringItUp(arr){
  // your code here
}

console.log(stringItUp([2, 5, 100])); // ["2", "5", "100"]

Answer:

function stringItUp(arr){
  let strArr = arr.map(String);
  return strArr;
}

console.log(stringItUp([2, 5, 100])); 

Here is another solution of converting int array to string array.

var arr = [2, 5, 100];
var strArr = arr.map(function(e){return e.toString()});
console.log(strArr); //

However, From my point of view, better to use arr.map(String).

3. Capitalize each of an array of names

function capitalizeNames(arr){
  // your code here
}

console.log(capitalizeNames(["john", "JACOB", "jinGleHeimer", "schmidt"])); 
// ["John", "Jacob", "Jingleheimer", "Schmidt"]

Answer

function capitalizeNames(arr){
  let uppClassArr=arr.map(function(string){
    return string.substr(0,1).toUpperCase() + string.substr(1).toLowerCase();
  })
  return uppClassArr
}

console.log(capitalizeNames(["john", "JACOB", "jinGleHeimer", "schmidt"])); 

Notification (idea steps):
Here is a point that string arrays that we have is random, which means the name

1. Capitalize the string;
2. converting the letter [1, end] to the lowercase.

if you do this:

function capitalizeNames(arr){
  let uppClassArr=arr.map(function(string){
    return string.toUpperCase() 
  })
  return uppClassArr
}

console.log(capitalizeNames(["john", "JACOB", "jinGleHeimer", "schmidt"])); 

Result would like this:

[ 'JOHN', 'JACOB', 'JINGLEHEIMER', 'SCHMIDT' ]

4. Make an array of strings of the names

function namesOnly(arr){
  // your code here
}

console.log(namesOnly([
    {
        name: "Angelina Jolie",
        age: 80
    },
    {
        name: "Eric Jones",
        age: 2
    },
    {
        name: "Paris Hilton",
        age: 5
    },
    {
        name: "Kayne West",
        age: 16
    },
    {
        name: "Bob Ziroll",
        age: 100
    }
])); 
// ["Angelina Jolie", "Eric Jones", "Paris Hilton", "Kayne West", "Bob Ziroll"]

Answer:

function namesOnly(arr){
  let onlyNameArr = arr.map(x=>x.name);
  return onlyNameArr;
}

console.log(namesOnly([
    {
        name: "Angelina Jolie",
        age: 80
    },
    {
        name: "Eric Jones",
        age: 2
    },
    {
        name: "Paris Hilton",
        age: 5
    },
    {
        name: "Kayne West",
        age: 16
    },
    {
        name: "Bob Ziroll",
        age: 100
    }
]));

5. Make an array of strings of the names saying whether or not they can go to The Matrix

function makeStrings(arr){
  // your code here
}

console.log(makeStrings([
    {
        name: "Angelina Jolie",
        age: 80
    },
    {
        name: "Eric Jones",
        age: 2
    },
    {
        name: "Paris Hilton",
        age: 5
    },
    {
        name: "Kayne West",
        age: 16
    },
    {
        name: "Bob Ziroll",
        age: 100
    }
])); 
// ["Angelina Jolie can go to The Matrix", 
// "Eric Jones is under age!!", 
// "Paris Hilton is under age!!", 
// "Kayne West is under age!!", 
// "Bob Ziroll can go to The Matrix"]

Answer:

function makeStrings(arr){
  let reFormArr = arr.map(arr =>{
    if(arr.age>=18){
      console.log(arr.name + ' can go to The Matrix') 
    }else {
        console.log(arr.name + " is under age!!");
      }
  })
}

Hints: Using map to reformat objects in an array
reference:
6) Make an array of the names in h1s, and the ages in h2s

function readyToPutInTheDOM(arr){
  // your code here
}
console.log(readyToPutInTheDOM([
    {
        name: "Angelina Jolie",
        age: 80
    },
    {
        name: "Eric Jones",
        age: 2
    },
    {
        name: "Paris Hilton",
        age: 5
    },
    {
        name: "Kayne West",
        age: 16
    },
    {
        name: "Bob Ziroll",
        age: 100
    }
])); 
// ["<h1>Angelina Jolie</h1><h2>80</h2>", 
// "<h1>Eric Jones</h1><h2>2</h2>", 
// "<h1>Paris Hilton</h1><h2>5</h2>", 
// "<h1>Kayne West</h1><h2>16</h2>", 
// "<h1>Bob Ziroll</h1><h2>100</h2>"]

Answer:

function readyToPutInTheDOM(arr){
    let reFormArr = arr.map(arr =>{
      console.log('<h1>'+arr.name+'</h1>'+"<h2>"+arr.age+'</h2>')
  })
}