1- What is JavaScript?
JavaScript is a scripting language most often used for client-side web development.
2- What is the difference between JavaScript and Jscript?
Both JavaScript and Jscript are almost similar. JavaScript was developed by Netscape. Microsoft reverse engineered Javascript and called it JScript.
3- How do we add JavaScript onto a web page?
Ans:There are several way for adding JavaScript on a web page, but there are two ways which are commonly used by developers
If your script code is very short and only for single page, then following ways are the best:
a) You can place <script type="text/javascript"> tag inside the <head> element.
Code
<head>
<title>Page Title</title>
<script language="JavaScript" type="text/javascript">
var name = "Vikas Ahlawta"
alert(name);
</script>
</head>
b) If your script code is very large, then you can make a JavaScript file and add its path in the following way:
Code
<head>
<title>Page Title</title>
<script type="text/javascript" src="myjavascript.js"></script>
</head>
4. Is JavaScript case sensitive?
Yes!
A function getElementById is not the same as getElementbyID.
5- What are the types used in JavaScript?
String, Number, Boolean, Function, Object, Null, Undefined.
6. What are the boolean operators supported by JavaScript? And Operator: &&
Or Operator: ||
Not Operator: !
7-What is the difference between “==” and “===”?
Ans:
“==” checks equality only,
“===” checks for equality as well as the type.
8. How to access the value of a textbox using JavaScript?
Code
<!DOCTYPE html>
<html>
<body>
Full name: <input type="text" id="txtFullName"
name="FirstName" value="Vikas Ahlawat">
</body>
</html>
There are following ways to access the value of the above textbox:
var name = document.getElementById('txtFullName').value;
alert(name);
or:
we can use the old way:
document.forms[0].mybutton.
var name = document.forms[0].FirstName.value;
alert(name);
Note: This uses the "name" attribute of the element to locate it.
9. What are the ways of making comments in JavaScript?
Ans:
// is used for line comments
ex:- var x=10; //comment text
/*
*/ is used for block comments
ex:-
var x= 10; /* this is
block comment example.*/
10. How will you get the Checkbox status whether it is checked or not?
Ans:
var status = document.getElementById('checkbox1').checked;
alert(status);
will return true or false.
11. How to create arrays in JavaScript?
There are two ways to create array in JavaScript like other languages:
a) The first way to create array
Declare Array:
Code
var names = new Array();
Add Elements in Array:-
names[0] = "Vikas";
names[1] = "Ashish";
names[2] = "Nikhil";
b) This is the second way:
var names = new Array("Vikas", "Ashish", "Nikhil");
12. If an array with name as "names" contain three elements, then how will you print the third element of this array?
Ans: Print third array element document.write(names[2]);
Note:- Array index starts with 0.
13. How do you submit a form using JavaScript?
Ans:Use document.forms[0].submit();
14. What does isNaN function do?
Ans: It returns true if the argument is not a number.
Example:
Code
document.write(isNaN("Hello")+ "<br>");
document.write(isNaN("2013/06/23")+ "<br>");
document.write(isNaN(123)+ "<br>");
The output will be:
true
true
false
15. What is the use of Math Object in JavaScript?
Ans: The math object provides you properties and methods for mathematical constants and functions.
ex:-
Code
var x = Math.PI; // Returns PI
var y = Math.sqrt(16); // Returns the square root of 16
var z = Math.sin(90); Returns the sine of 90
16. What do you understand by this keyword in JavaScript?
Ans:"this" keyword refers to the current object like other language.
17. What does "1"+2+4 evaluate to?
Ans: Since 1 is a string, everything is a string, so the result is 124.
18. What does 3+4+"7" evaluate to?
Ans: Since 3 and 4 are integers, this is number arithmetic, since 7 is a string, it is concatenation, so 77 is the result.
19) How do you change the style/class on any element using JavaScript?
Ans:
Code
document.getElementById(“myText”).style.fontSize = “10";
-or-
document.getElementById(“myText”).className = “anyclass”;
20. Does JavaScript support foreach loop?
Ans: No.
21. What looping structures are there in JavaScript?
Ans: for, while, do-while loops
22. What is an object in JavaScript, give an example?
Ans: An object is just a container for a collection of named values:
// Create the man object
Code
var man = new Object();
man.name = 'Vikas Ahlawat';
man.living = true;
man.age = 27;
23. How you will add function as a property in a JavaScript object? Give an example.
Code
var man = new Object();
man.name = 'Vikas Ahlawat';
man.living = true;
man.age = 27;
man.getName = function() { return man.name;}
console.log(man.getName()); // Logs 'Vikas Ahlawat'.
24. What is the similarity between the 1st and 2nd statement?
1st:- var myString = new String('male'); // An object.
2nd:- var myStringLiteral = 'male'; // Primitive string value, not an object.
Ans: Both will call String() constructor function
You can confirm it by running the following statement:
console.log(myString.constructor, myStringLiteral.constructor);
25. What will be the output of the following statements?
Code
var myString = 'Vikas' // Create a primitive string object.
var myStringCopy = myString; // Copy its value into a new variable.
var myString = null; // Manipulate the value
console.log(myString, myStringCopy);
Ans: // Logs 'null Vikas'
26. Consider the following statements and tell what would be the output of the logs statements?
var price1 = 10;
var price2 = 10;
var price3 = new Number('10'); // A complex numeric object because new was used.
console.log(price1 === price2);
console.log(price1 === price3);
Ans:
console.log(price1 === price2); // Logs true.
console.log(price1 === price3); /* Logs false because price3
contains a complex number object and price 1
is a primitive value. */
27. What would be the output of the following statements?
var object1 = { same: 'same' };
var object2 = { same: 'same' };
console.log(object1 === object2);
Logs false, JavaScript does not care that they are identical and of the same object type.
When comparing complex objects, they are equal only when they reference the same object (i.e., have the same address). Two variables containing identical objects are not equal to each other since they do not actually point at the same object.
28- What would be the output of the following statements?
Code
var object1 = { same: 'same' };
var object2 = object1;
console.log(object1 === object2);
Logs true
29. What is this? var myArray = [[[]]];
Three dimensional array
30. Name any two JavaScript functions which are used to convert nonnumeric values into numbers?
Number()
parseInt()
parseFloat()
Code
var n1 = Number(“Hello world!”); //NaN
var n2 = Number(“”); //0
var n3 = Number(“000010”); //10
var n4 = Number(true); //1
var n5 = Number(NaN); //NaN
31.What is relationship between JavaScript and ECMAScript?
ECMAScript is yet another name for JavaScript (other names include LiveScript). The current JavaScript that you see supported in browsers is ECMAScript revision 3.
32.What does undefined value mean in javascript?
Undefined value means the variable used in the code doesnt exist or is not assigned any value or the property doesnt exist.
33.How to hide javascript code from old browsers that dont run it?
Use the below specified style of comments
<script language=javascript>
<!--
javascript code goes here
// -->
34.What does the "Access is Denied" IE error mean?
The "Access Denied" error in any browser is due to the following reason.
A javascript in one window or frame is tries to access another window or frame whose
document's domain is different from the document containing the script.
35.What is the difference between undefined value and null value?
(i)Undefined value cannot be explicitly stated that is there is no keyword called undefined whereas null value has keyword called null
(ii)typeof undefined variable or property returns undefined whereas
typeof null value returns object
36.How to detect the operating system on the client machine?
In order to detect the operating system on the client machine, the navigator.appVersion
string (property) should be used.
JavaScript is a scripting language most often used for client-side web development.
2- What is the difference between JavaScript and Jscript?
Both JavaScript and Jscript are almost similar. JavaScript was developed by Netscape. Microsoft reverse engineered Javascript and called it JScript.
3- How do we add JavaScript onto a web page?
Ans:There are several way for adding JavaScript on a web page, but there are two ways which are commonly used by developers
If your script code is very short and only for single page, then following ways are the best:
a) You can place <script type="text/javascript"> tag inside the <head> element.
Code
<head>
<title>Page Title</title>
<script language="JavaScript" type="text/javascript">
var name = "Vikas Ahlawta"
alert(name);
</script>
</head>
b) If your script code is very large, then you can make a JavaScript file and add its path in the following way:
Code
<head>
<title>Page Title</title>
<script type="text/javascript" src="myjavascript.js"></script>
</head>
4. Is JavaScript case sensitive?
Yes!
A function getElementById is not the same as getElementbyID.
5- What are the types used in JavaScript?
String, Number, Boolean, Function, Object, Null, Undefined.
6. What are the boolean operators supported by JavaScript? And Operator: &&
Or Operator: ||
Not Operator: !
7-What is the difference between “==” and “===”?
Ans:
“==” checks equality only,
“===” checks for equality as well as the type.
8. How to access the value of a textbox using JavaScript?
Code
<!DOCTYPE html>
<html>
<body>
Full name: <input type="text" id="txtFullName"
name="FirstName" value="Vikas Ahlawat">
</body>
</html>
There are following ways to access the value of the above textbox:
var name = document.getElementById('txtFullName').value;
alert(name);
or:
we can use the old way:
document.forms[0].mybutton.
var name = document.forms[0].FirstName.value;
alert(name);
Note: This uses the "name" attribute of the element to locate it.
9. What are the ways of making comments in JavaScript?
Ans:
// is used for line comments
ex:- var x=10; //comment text
/*
*/ is used for block comments
ex:-
var x= 10; /* this is
block comment example.*/
10. How will you get the Checkbox status whether it is checked or not?
Ans:
var status = document.getElementById('checkbox1').checked;
alert(status);
will return true or false.
11. How to create arrays in JavaScript?
There are two ways to create array in JavaScript like other languages:
a) The first way to create array
Declare Array:
Code
var names = new Array();
Add Elements in Array:-
names[0] = "Vikas";
names[1] = "Ashish";
names[2] = "Nikhil";
b) This is the second way:
var names = new Array("Vikas", "Ashish", "Nikhil");
12. If an array with name as "names" contain three elements, then how will you print the third element of this array?
Ans: Print third array element document.write(names[2]);
Note:- Array index starts with 0.
13. How do you submit a form using JavaScript?
Ans:Use document.forms[0].submit();
14. What does isNaN function do?
Ans: It returns true if the argument is not a number.
Example:
Code
document.write(isNaN("Hello")+ "<br>");
document.write(isNaN("2013/06/23")+ "<br>");
document.write(isNaN(123)+ "<br>");
The output will be:
true
true
false
15. What is the use of Math Object in JavaScript?
Ans: The math object provides you properties and methods for mathematical constants and functions.
ex:-
Code
var x = Math.PI; // Returns PI
var y = Math.sqrt(16); // Returns the square root of 16
var z = Math.sin(90); Returns the sine of 90
16. What do you understand by this keyword in JavaScript?
Ans:"this" keyword refers to the current object like other language.
17. What does "1"+2+4 evaluate to?
Ans: Since 1 is a string, everything is a string, so the result is 124.
18. What does 3+4+"7" evaluate to?
Ans: Since 3 and 4 are integers, this is number arithmetic, since 7 is a string, it is concatenation, so 77 is the result.
19) How do you change the style/class on any element using JavaScript?
Ans:
Code
document.getElementById(“myText”).style.fontSize = “10";
-or-
document.getElementById(“myText”).className = “anyclass”;
20. Does JavaScript support foreach loop?
Ans: No.
21. What looping structures are there in JavaScript?
Ans: for, while, do-while loops
22. What is an object in JavaScript, give an example?
Ans: An object is just a container for a collection of named values:
// Create the man object
Code
var man = new Object();
man.name = 'Vikas Ahlawat';
man.living = true;
man.age = 27;
23. How you will add function as a property in a JavaScript object? Give an example.
Code
var man = new Object();
man.name = 'Vikas Ahlawat';
man.living = true;
man.age = 27;
man.getName = function() { return man.name;}
console.log(man.getName()); // Logs 'Vikas Ahlawat'.
24. What is the similarity between the 1st and 2nd statement?
1st:- var myString = new String('male'); // An object.
2nd:- var myStringLiteral = 'male'; // Primitive string value, not an object.
Ans: Both will call String() constructor function
You can confirm it by running the following statement:
console.log(myString.constructor, myStringLiteral.constructor);
25. What will be the output of the following statements?
Code
var myString = 'Vikas' // Create a primitive string object.
var myStringCopy = myString; // Copy its value into a new variable.
var myString = null; // Manipulate the value
console.log(myString, myStringCopy);
Ans: // Logs 'null Vikas'
26. Consider the following statements and tell what would be the output of the logs statements?
var price1 = 10;
var price2 = 10;
var price3 = new Number('10'); // A complex numeric object because new was used.
console.log(price1 === price2);
console.log(price1 === price3);
Ans:
console.log(price1 === price2); // Logs true.
console.log(price1 === price3); /* Logs false because price3
contains a complex number object and price 1
is a primitive value. */
27. What would be the output of the following statements?
var object1 = { same: 'same' };
var object2 = { same: 'same' };
console.log(object1 === object2);
Logs false, JavaScript does not care that they are identical and of the same object type.
When comparing complex objects, they are equal only when they reference the same object (i.e., have the same address). Two variables containing identical objects are not equal to each other since they do not actually point at the same object.
28- What would be the output of the following statements?
Code
var object1 = { same: 'same' };
var object2 = object1;
console.log(object1 === object2);
Logs true
29. What is this? var myArray = [[[]]];
Three dimensional array
30. Name any two JavaScript functions which are used to convert nonnumeric values into numbers?
Number()
parseInt()
parseFloat()
Code
var n1 = Number(“Hello world!”); //NaN
var n2 = Number(“”); //0
var n3 = Number(“000010”); //10
var n4 = Number(true); //1
var n5 = Number(NaN); //NaN
31.What is relationship between JavaScript and ECMAScript?
ECMAScript is yet another name for JavaScript (other names include LiveScript). The current JavaScript that you see supported in browsers is ECMAScript revision 3.
32.What does undefined value mean in javascript?
Undefined value means the variable used in the code doesnt exist or is not assigned any value or the property doesnt exist.
33.How to hide javascript code from old browsers that dont run it?
Use the below specified style of comments
<script language=javascript>
<!--
javascript code goes here
// -->
34.What does the "Access is Denied" IE error mean?
The "Access Denied" error in any browser is due to the following reason.
A javascript in one window or frame is tries to access another window or frame whose
document's domain is different from the document containing the script.
35.What is the difference between undefined value and null value?
(i)Undefined value cannot be explicitly stated that is there is no keyword called undefined whereas null value has keyword called null
(ii)typeof undefined variable or property returns undefined whereas
typeof null value returns object
36.How to detect the operating system on the client machine?
In order to detect the operating system on the client machine, the navigator.appVersion
string (property) should be used.
Useful blog admin, this is what I have looked for. Keep sharing more interview questions with answers.
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