JavaScript interview questions and answers

1.    What's 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.
2.    What are JavaScript types? - Number, String, Boolean, Function, Object, Null, Undefined.
3.    How do you convert numbers between different bases in JavaScript? - Use the parseInt() function, that takes a string as the first parameter, and the base as a second parameter. So to convert hexadecimal 3F to decimal, use parseInt ("3F", 16);
4.    What does isNaN function do? - Return true if the argument is not a number.
5.    What is negative infinity? - It's a number in JavaScript, derived by dividing negative number by zero.
6.    What boolean operators does JavaScript support? - &&, || and !
7.    What does "1"+2+4 evaluate to? - Since 1 is a string, everything is a string, so the result is 124.
8.    How about 2+5+"8"? - Since 2 and 5 are integers, this is number arithmetic, since 8 is a string, it's concatenation, so 78 is the result.
9.    What looping structures are there in JavaScript? - for, while, do-while loops, but no foreach.
10.    How do you create a new object in JavaScript? - var obj = new Object(); or var obj = {};
11.    How do you assign object properties? - obj["age"] = 17 or obj.age = 17.
12.    What's a way to append a value to an array? - arr[arr.length] = value;
13.    What is this keyword? - It refers to the current object.
14.    1.  Why so JavaScript and Java have similar name?
15.    A.  JavaScript is a stripped-down version of Java
16.    B.  JavaScript's syntax is loosely based on Java's
17.    C.  They both originated on the island of Java
18.    D.  None of the above
19.   
20.    2.  When a user views a page containing a JavaScript program, which machine actually executes the script?
21.    A.  The User's machine running a Web browser
22.    B.   The Web server
23.    C.  A central machine deep within Netscape's corporate offices
24.    D.  None of the above
25.   
26.    3.  ______ JavaScript is also called client-side JavaScript.
27.    A.  Microsoft
28.    B.  Navigator
29.    C.  LiveWire
30.    D.  Native
31.   
32.    4.  __________ JavaScript is also called server-side JavaScript.
33.    A.  Microsoft
34.    B.   Navigator
35.    C.  LiveWire
36.    D.  Native
37.   
38.    5.  What are variables used for in JavaScript Programs?
39.    A.  Storing numbers, dates, or other values
40.    B.   Varying randomly
41.    C.  Causing high-school algebra flashbacks
42.    D.  None of the above
43.   
44.    6.  _____ JavaScript statements embedded in an HTML page can respond to user events such as mouse-clicks, form input, and page navigation.
45.    A.  Client-side
46.    B.   Server-side
47.    C.  Local
48.    D.  Native
49.   
50.    7.  What should appear at the very end of your JavaScript?
51.    The
53.    B.    The
104.    D. 
105.   
106.    16.  Inside which HTML element do we put the JavaScript?
107.    A. 
108.    B.  
109.    C.  



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