JavaScript_Assessment2

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Question:1

How do you check if an element exists in an array?

// To check if an element exists in an array
const arr = [1,3,5,6,7,8,9,10,11,12]
console.log(arr.includes(9));

// Check if an element does not exist in an array

const arr1 =[1,3,5,6,7,8,9,10,11,12]
console.log(arr.includes(2));

// Output:
mac@macs-MacBook-Pro JavaScript_Assessment2 % node index.js
true
false

Explanation:

• We can use the includes() method in JavaScript to check if an item exists in an array

• The includes() method returns true if an array contains a specified value.

• The includes() method returns false if the value is not found.

• The includes() method is case sensitive.

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Question:2

What is the difference between .map() and .forEach()?

• Explanation: The map method receives a function as a parameter. Then it applies it on each element and returns an entirely new array populated with the results of calling the provided function. This means that it returns a new array that contains an image of each element of the array. It will always return the same number of items.

// Use case of Map function
const arr = [5, 4, 3, 2, 1]
console.log(arr.map(x => x * x));

// Output:
mac@macs-MacBook-Pro JavaScript_Assessment2 % node index.js
[ 25, 16, 9, 4, 1 ]

• Like map , the forEach() method receives a function as an argument and executes it once for each array element. However, instead of returning a new array like map, it returns undefined.

// use case of forEach() function

const arr = [
  { id: 1, name: "Shivam" },
  { id: 2, name: "Kaif" },
  { id: 3, name: "Shubham" },
]

arr.forEach(element => console.log(element.name))

// Output:
mac@macs-MacBook-Pro JavaScript_Assessment2 % node index.js
Shivam
Kaif
Shubham

• Difference between map() and forEach() is the returning value. The forEach() method returns undefined and map() returns a new array with the transformed elements. Even if they do the same job, the returning value remains different.

const arr = [1, 2, 3, 4, 5]
console.log(arr.forEach(x => x * x));
console.log(arr.map(x => x * x));

//Output
mac@macs-MacBook-Pro JavaScript_Assessment2 % node index.js
undefined
[ 1, 4, 9, 16, 25 ]

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Question 3

What is the difference between .filter() and .find()?

Explanation: First We see that what they are filter() method

• This method returns all the elements of the array that satisfy the condition specified in the callback function. Example:

const x = [1, 2, 3, 4, 5];
const y = x.filter(x => x * 2 === 2);
console.log(y);

//Output
mac@macs-MacBook-Pro JavaScript_Assessment2 % node index.js                  
[ 1 ]

• If you check out the output of the above example, the value of y is an array of 1 element that satisfies the condition. This is because the filter() method iterates over all elements of the array and then returns a filtered array which satisfy the condition specified.
• Now , Moving On Next Method What is the find() method?
• This method returns first element of the array that satisfies the condition specified in the callback function. Example:

const x = [1, 2, 3, 4, 5];
const y = x.find(x => x * 2 === 2);
console.log(y);

// Output:
mac@macs-MacBook-Pro JavaScript_Assessment2 % node index.js
1

• Now, if we see the output of the example, the value of y is 1. This is because the find() method searches for first element in the array that satisfies the condition specified.

• The main differences between above examples is:

• 1. filter() returns an array containing the element that satisfies the condition, but find() returns the element itself that satisfies the condition.
• 2. In filter(), whole array is iterated despite the fact that the element being searched for is present at the beginning. But in find(), as soon as the element that satisfies the condition is found, it gets returned.

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Question 4

How do we check if a key exists in a JavaScript object?

Explanation: We can use the JavaScript inoperator to check if a specified property/key exists in an object. It has a straightforward syntax and returns true if the specified property/key does not exists it return false.

• The syntax when using the in operator is:

'keys' in obj

• Suppose we have an object which contains a user's details:

let user = {
  name: "Shivam Shukla",
  age: 23
};
console.log('name' in user); // Returns true
console.log('birth' in user);// Returns false

// Output
mac@macs-MacBook-Pro JavaScript_Assessment2 % node index.js
true
false

Here If key exist it return true otherwise false .

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Question 5

What is the output of the following code? Why?

var a = 3; 
var b = { a: 9, b: ++a }; 
console.log(a + b.a + ++b.b);

// Output
mac@macs-MacBook-Pro JavaScript_Assessment2 % node index.js                  
18

• Explanation: Prefix operator increments the number and then returns it. So the following expression will be calculated as 4 + 9 + 5 = 18

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Question 6

What is the output of the following code? Why?

const arrayOfOddNumbers = [1, 3, 5]; 
arrayOfOddNumbers[100] = 199; 
console.log(arrayOfOddNumbers.length);

// Output
mac@macs-MacBook-Pro JavaScript_Assessment2 % node index.js
101

• Explanation: The reason for this solution is as follows: JavaScript places empty as a value for indices 3 - 99. That's why, when we set the value of the 100th index, the array looks like:

    [1, 3, 5 , empty x 97 , 199]

We get the lenght as 101

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Question 7

What is the output of the following code? Why?

function checkAge(data) { 
    if (data === { age: 18 }) 
       { 
         console.log('You are an adult!'); 
       }
   else if (data == { age: 18 }) 
       { 
         console.log('You are still an adult.'); 
       } else { 
           console.log(`Hmm.. You don't have an age I guess`); 
       } 
      } 
    checkAge({ age: 18 });
// Output 
 mac@macs-MacBook-Pro JavaScript_Assessment2 % node index.js
 Hmm.. You don't have an age I guess

• Explanation When testing equality, primitives are compared by their value, while objects are compared by their reference. JavaScript checks if the objects have a reference to the same location in memory.

The two objects that we are comparing don't have that: the object we passed as a parameter refers to a different location in memory than the object we used in order to check equality.

This is why both { age: 18 } === { age: 18 } and { age: 18 } == { age: 18 } return false.

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Question 8

Remove Duplicate Items from Array using reduce function.

Explanation:

let arr = ["shivam", "shubham", "danish",
"saurabh", "shivam", "kaif", "shubham", "danish"];

function removeDuplicates(arr) {
let unique = arr.reduce(function (acc, curr) {
if (!acc.includes(curr))
    acc.push(curr);
return acc;
}, []);
return unique;
}
console.log(removeDuplicates(arr));
// Output:
mac@macs-MacBook-Pro JavaScript_Assessment2 % node index.js
[ 'shivam', 'shubham', 'danish', 'saurabh', 'kaif' ]

• In the reduce() method, the array elements are reduced and combined into a final array based on the reducer function we pass.

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Question 9

Sort an array of strings by length.

Input: ["Testing", "The", "Code"]
Output: [“The", "Code", "Testing"]

// Code 

const arr = ["Testing", "The", "Code"]
arr.sort(function(a, b){
    return a.length - b.length;
  });
console.log(arr);

// Output:
mac@macs-MacBook-Pro JavaScript_Assessment2 % node index.js     
[ 'The', 'Code', 'Testing' ]

• Explanation - In this Simple way we use sort() method on the arr of strings . The sort method takes comparison function as an argument , which compares two element of the array and determines their order. this comparison fn (a,b) => a.length - b.length compares the lenght by subtraction , we got ascending order based on string.

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Question 10

Write a JavaScript function to check whether an input is an array or not.

Explanation: In JS we check variable is an array by using 3 methods , these are:

• Using isArray() method
• Using instanceof operator
• Using checking the constructor type

Method 1. isArray() Method

Example 1: In this example, we will check if a given variable is an array or not using the isArray() method in JavaScript.

function checkArray() {
  let str = "This is a string";
  let arr = [10, 20, 30, 40];

  let ans = Array.isArray(str);
  console.log("Output for String: " + ans);
  ans = Array.isArray(arr);
  console.log("Output for Array: " + ans);
}

checkArray();

// Output
mac@macs-MacBook-Pro JavaScript_Assessment2 % node index.js
Output for String: false
Output for Array: true

• It returns a true boolean value if the variable is an array and a false if it is not.

Method 2 Using JavaScript instanceof operator

• Example: In this example, we will check if a given variable is an array or not using the instanceof operator in JavaScript.

function checkArray() {
  let str = "This is a string";
  let arr = [10, 20, 30, 40];

  let ans = str instanceof Array;
  console.log("Output for String: " + ans);
  ans = arr instanceof  Array;
  console.log("Output for Array: " + ans);
}

checkArray();

// Output
mac@macs-MacBook-Pro JavaScript_Assessment2 % node index.js
Output for String: false
Output for Array: true

• It returns a true boolean value if the variable is an array and a false if it is not.

Method 3: Checking the constructor property of the variable

Example 3: In this example, we will check if a given variable is an array or not using the constructor method in JavaScript.

function checkArray() {
  let str = "This is a string";
  let arr = [10, 20, 30, 40];

  let ans = str.constucture === Array;
  console.log("Output for String: " + ans);
  ans = arr.constucture ===  Array;
  console.log("Output for Array: " + ans);
}

checkArray();
// Output
mac@macs-MacBook-Pro JavaScript_Assessment2 % node index.js
Output for String: false
Output for Array: true

• It returns a true boolean value if the variable is an array and a false if it is not.

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Question 11

Write a JavaScript function to sort the following array of objects by title value.

Sample object :

var library = [ { author: 'Bill Gates', title: 'The Road Ahead', libraryID: 1254}, { author: 'Steve Jobs', title: 'Walter Isaacson', libraryID: 4264}, { author: 'Suzanne Collins', title: 'Mockingjay: The Final Book of The Hunger Games', libraryID: 3245} ];

   var library = [
 { author: "Bill Gates", title: "The Road Ahead", libraryID: 1254 },
 { author: "Steve Jobs", title: "Walter Isaacson", libraryID: 4264 },
 {
   author: "Suzanne Collins",
   title: "Mockingjay: The Final Book of The Hunger Games",
   libraryID: 3245,
 },
];
let sortByTitle = library.sort((a,b) => a.title > b.title ? 1 : -1);  // Sort() method to sort array of objects by title value
console.log(sortByTitle);

// Output
mac@macs-MacBook-Pro JavaScript_Assessment2 % node index.js
[
 {
   author: 'Suzanne Collins',
   title: 'Mockingjay: The Final Book of The Hunger Games',
   libraryID: 3245
 },
 { author: 'Bill Gates', title: 'The Road Ahead', libraryID: 1254 },
 { author: 'Steve Jobs', title: 'Walter Isaacson', libraryID: 4264 }
]

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Question 12

Write a program to derive the provided output:-

• Input: var arrOfObj=[{name: 'Rohan', physics: 20, chemistry: 18, math: 26}, {name: 'Geeta', physics: 29, chemistry: 30, math: 22}, {name: 'Kunal', physics: 27, chemistry: 25, math: 21}, {name: 'Abhishek', physics: 21, chemistry: 26, math: 23}, {name: 'Aashish', physics: 25, chemistry: 16, math: 18}];
• Output: { Rohan: 64, Geeta: 81, Kunal: 73, Abhishek: 70, Aashish: 59 }

var arrOfObj = [
 { name: "Rohan", physics: 20, chemistry: 18, math: 26 },
 { name: "Geeta", physics: 29, chemistry: 30, math: 22 },
 { name: "Kunal", physics: 27, chemistry: 25, math: 21 },
 { name: "Abhishek", physics: 21, chemistry: 26, math: 23 },
 { name: "Aashish", physics: 25, chemistry: 16, math: 18 },
];
var totalMarks = {};

for (var i = 0; i < arrOfObj.length; i++) {
 var student = arrOfObj[i];
 var total = student.physics + student.chemistry + student.math; // Adding Marks of student
 totalMarks[student.name] = total;
}

console.log(totalMarks);

// Output
mac@macs-MacBook-Pro JavaScript_Assessment2 % node index.js                  
{ Rohan: 64, Geeta: 81, Kunal: 73, Abhishek: 70, Aashish: 59 }

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Question 13

Write a JavaScript function to filter false, null, 0 and blank values from an array.

Input: [“Test”, true, null, false, 0] Output: [“Test”, true]

function filterValues(array) {
   return array.filter((item) => item ); // filtered Null ,false , 0
   }
   var array =  ["Test", true, null, false, 0]
   console.log(filterValues(array));  
// Output
 vmac@macs-MacBook-Pro JavaScript_Assessment2 % node index.js
 [ 'Test', true ]

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Question 14

Write a JavaScript program to count the number of arrays inside a given array.

Input: [2,8,[6],3,3,5,3,4,[5,4]] Output: 2

const countArrays = (arr) => {
let count = 0;
for (let i = 0; i < arr.length; i++) {
  if (Array.isArray(arr[i])) {  // Count no. of array
    count++;
  }
}
return count;
};

console.log(countArrays([2, 8, [6], 3, 3, 5, 3, 4, [5, 4]]));

// Output 
mac@macs-MacBook-Pro JavaScript_Assessment2 % node index.js
2 

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