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JavaScript Object - Exercises, Practice, Solution

JavaScript Object [18 exercises with solution]

[An editor is available at the bottom of the page to write and execute the scripts.]

1. Write a JavaScript program to list the properties of a JavaScript object. Go to the editor
Sample object:
var student = {
name : "David Rayy",
sclass : "VI",
rollno : 12 };
Sample Output: name,sclass,rollno
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2. Write a JavaScript program to delete the rollno property from the following object. Also print the object before or after deleting the property. Go to the editor
Sample object:
var student = {
name : "David Rayy",
sclass : "VI",
rollno : 12 };
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3. Write a JavaScript program to get the length of a JavaScript object. Go to the editor
Sample object :
var student = {
name : "David Rayy",
sclass : "VI",
rollno : 12 };
Click me to see the solution

4. Write a JavaScript program to display the reading status (i.e. display book name, author name and reading status) of the following books. Go to the editor

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

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5. Write a JavaScript program to get the volume of a Cylinder with four decimal places using object classes. Go to the editor
Volume of a cylinder : V = πr2h
where r is the radius and h is the height of the cylinder.
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6. Write a Bubble Sort algorithm in JavaScript. Go to the editor
Note : Bubble sort is a simple sorting algorithm that works by repeatedly stepping through the list to be sorted,
Sample Data: [6,4,0, 3,-2,1]
Expected Output : [-2, 0, 1, 3, 4, 6]
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7. Write a JavaScript program which returns a subset of a string. Go to the editor
Sample Data: dog
Expected Output: ["d", "do", "dog", "o", "og", "g"]
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8. Write a JavaScript program to create a Clock. Go to the editor
Note: The output will come every second.
Expected Console Output :
"14:37:42"
"14:37:43"
"14:37:44"
"14:37:45"
"14:37:46"
"14:37:47"
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9. Write a JavaScript program to calculate the area and perimeter of a circle. Go to the editor
Note : Create two methods to calculate the area and perimeter. The radius of the circle will be supplied by the user.
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10. Write a JavaScript program to sort an array of JavaScript objects. Go to the editor
Sample Object :

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

Expected Output:

[[object Object] {
  author: "Walter Isaacson",
  libraryID: 4264,
  title: "Steve Jobs"
}, [object Object] {
  author: "Suzanne Collins",
  libraryID: 3245,
  title: "Mockingjay: The Final Book of The Hunger Games"
}, [object Object] {
  author: "The Road Ahead",
  libraryID: 1254,
  title: "Bill Gates"
}]

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11. Write a JavaScript function to print all the methods in an JavaScript object. Go to the editor
Test Data :
console.log(all_properties(Array));
["length", "name", "arguments", "caller", "prototype", "isArray", "observe", "unobserve"]
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12. Write a JavaScript function to parse an URL. Go to the editor
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13. Write a JavaScript function to retrieve all the names of object's own and inherited properties. Go to the editor
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14. Write a JavaScript function to retrieve all the values of an object's properties. Go to the editor
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15. Write a JavaScript function to convert an object into a list of `[key, value]` pairs. Go to the editor
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16. Write a JavaScript function to get a copy of the object where the keys have become the values and the values the keys. Go to the editor
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17. Write a JavaScript function to check whether an object contains given property. Go to the editor
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18. Write a JavaScript function to check whether a given value is a DOM element. Go to the editor
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More to Come !

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Live Demo:

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Do not submit any solution of the above exercises at here, if you want to contribute go to the appropriate exercise page.



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JavaScript: Tips of the Day

instance

class Calc {
	constructor() {
		this.count = 0 
	}

	increase() {
		this.count ++
	}
}

const calc = new Calc()
new Calc().increase()

console.log(calc.count)

We set the variable calc equal to a new instance of the Calc class. Then, we instantiate a new instance of Calc, and invoke the increase method on this instance. Since the count property is within the constructor of the Calc class, the count property is not shared on the prototype of Calc. This means that the value of count has not been updated for the instance calc points to, count is still 0.

Ref: https://bit.ly/2Hcpkm6