JavaScript Test Preparation

Doncho Minkov

Telerik Software Academyacademy.telerik.com

Technical Trainer

http://telerikacademy.com

Data Types

3

Question What is the value of the variable

date after the assignment?

a) undefined

b) 2 May 2013

c) null

d) 16 February 2012

e) the code will throw an exception

f) 2 April 2013

g) 2 December 2013

var date = new Date(2012, 16, 2);

Answer Months in Javascript are assigned from index 0 If we order all months, their

"indices" will be: 0 -> January

1 -> February

11 -> December)

We pass as a second argument in the Date object constructor a value greater than 11 JavaScript adds a whole year (2013) The remaining value 4 (= 16 months

– 12 months) is interpreted as May

4

What will be the result of the following code?

a) null

b) 1

c) NaN

d) Undefined

e) The code will throw an exception

f) 9007199254740992

var numberOne = 1;var nullValue = null;var result = numberOne + nullValue;document.writeln(result);

5

Question

Which expression should be used if we want to find the position at which the word "Telerik" appears in?

a) text.match("Telerik")

b) text.substring("Telerik")

c) text.find("Telerik")

d) text.indexOf("Telerik")

e) text.getPosition("Telerik")

f) text["Telerik"]

var text = "We all love Telerik Academy";

6

Question

What will be the result after executing the following code?

a) Number

b) Null

c) Object

d) NaN

e) Undefined

f) The code will throw an exception

var value = null;console.log(typeof value);

7

Question

Loops

8

What will be the output of the following source code? (ignore the time and time zone information)

a) undefined | 4 | undefined

b) January 1 2012 | 4 | telerik1

c) February 1 20121 | 4 | telerik1

d) Undefined | 4 | telerik1

e) January 1 2012 | 4 | telerik

f) January 1 20121 | 4 | telerik1

var container = [new Date(2012, 1, 1), 3, "telerik"];

for (i = 0; i < container.length; i++){ container[i] = container[i] + 1; document.write(container[i] + " | ");}

9

Question

Answer Since in JS value cannot be added to a date, it is interpreted as string So when we add the value "1" to the

date, "1" is appended to the string "February 1 2012"

The result of 3 + 1 is 4 When working with string, the operators "+" means concatenation JS interprets the value 1 as a string

"1" and appends it to "telerik", so it becomes "telerik1". 10

What is the output after executing the code:

a) 1 2 3 4 5 6 7 8 9 10 10

b) 10

c) 1 2 3 4 5 6 7 8 9 10 11

d) The code will throw an exception for misusing the "i" variable

e) 10 10 10 10 10 10 10 10 10 10 10

i = 10;for (var i = 1; i <= 10; i++){ document.write(i + " ");}document.write(i);

11

Question

Operators (without Bitwise)

a)2, 3, 3, 4, 4

b)2, 3, 3, 3, 4

c) 2, 2, 3, 3, 4

d)11, 11, 12, 13, 13

e)2, 2, 3, 4, 4

f) nothing will be printed

g)depends of the JS version

h)syntax error (the code is incorrect) 13

Question What will be the result of this

code?var a = 1, var b = 1;console.log( a + b );console.log( a + b++ );console.log( a + b );console.log( a + (++b) );console.log( a + b );

14

Question What will be the result of this

code?

a) 4 3

b) 4.0 3.0

c) 4 3.6666666666666665

d) 4.0 3.6666666666666665

e) 4 3.67

f) syntax error (the code is incorrect)

console.log(12 / 3); // result: 4console.log(11 / 3); // result: 3

15

Question What will be the result of this

code?

a) 0 0 0

b) 0.0 0.0 0.0

c) -Infinity, NaN, Infinity

d) -Infinity, Infinity, Infinity

e) runtime error: DivideByZeroException

f) syntax error (the code is incorrect)

console.log(-1.5 / 0.0); console.log(0.00 / 0.0);console.log(1.50 / 0.0);

a) false, false, false

b) true, true, true

c) true, true, false

d) null, true, null

e) true, true, null

f) null, null, null

g) false, false, true

h) 0, false, true

i) syntax error (the code is incorrect)

16

Question What will be the result of this

code?var a = null;console.log(!a);console.log(a || true);console.log(!a && false);

a) false, false, true, false, falseb) false, false, false, true, falsec) false, false, false, false, falsed) false, false, false, false, truee) syntax error (the code is incorrect)

17

Question What will be the result of this

code?var a = 1, b = true;console.log(a != b);console.log(a === b);console.log(!(a == a));console.log(a > b);console.log(a != b++);

a) 21, 23, 4b) 3, 4, 4c) 12, 13, 31d) 21, 23, 31e) 3, 5, 4f) syntax error (the code is incorrect)

18

Question What will be the result of this

code?var one = "2", two = "1", three = 3;console.log(one + two);console.log(one + three);console.log(three + 1);

a) a>b, number, 5, 33b) a>b, int, 5, 33c) a>b, number, 5.0, 33d) a>b, number, 5.0, 33.0e) a>b, integer, 5, 33f) syntax error (the code is incorrect)

19

Question What will be the result of this

code?var a = 6, b = 4;console.log(a > b ? "a>b" : "b>=a");console.log(typeof(2));console.log((a+b)/2);console.log(Number("33.00"));

a) NaNb) Infinityc) 314d) 628e) 3.14f) 6.28g) syntax error (the code is incorrect)

20

Question What will be the result of this

code?var r = 1 / (true + 1);var perimeter = 2 * Math.PI * r;console.log(Math.round(perimeter*100)/100);

Conditional Statements

22

Question What will be the result of this

code?

a)true

b)false

c) 0

d)1

e)nothing will be printed

f) syntax error (the code is incorrect)

var result = (5 <= 6) && (7 > 3) || (1 >= 2);if result console.log(!result);

23

Question What will be the result of this

code?

a)true, true

b)true, false

c) false, true

d)false, false

e)false

f) syntax error (the code is incorrect)

var a = true, b = false;console.log( !((a && b) + ', ' + (!a || !b)) );

24

Question What will be the result of this

code?

a)true

b)false

c) 0

d)1

e)syntax error (the code is incorrect)

var a=50, b="51";console.log(a<b - 1);

25

Question What will be the result of this

code?

a)50

b)51

c) true

d)false

e)syntax error (the code is incorrect)

var a=50, b=51;if (a>=b) console.log(a) else console.log(b);

26

Question What will be the result of this

code?

a)a < b == c

b)nothing will be printed

c) syntax error (the code is incorrect)

var a=1, b=2, c=1;if ((a < b) == c){ console.log("a < b == c");}

27

Question What will be the result of this

code?

a)X

b)Y

c) Z

d)err

e)syntax error (the code is incorrect)

var ch = 'y' - 1;if (ch == 'Y' || ch == 'y') console.log("Y");else if (ch == 'X' || ch == 'x') console.log("X");else if (ch == 'Z' || ch == 'z') console.log("E");else console.log("err");

a) Monday

b) Tuesday

c) Wednesday

d) Error!

e) syntax error (the code is incorrect) 28

Question What will be the result of this

code?int day = "Monday";switch (day){

case 1: console.log("Monday"); break;case 2: console.log("Tuesday"); break;case 3: console.log("Wednesday"); break;default: console.log("Error!"); break;

}

a) Monday

b) Tuesday

c) Wednesday

d) Error!

e) syntax error (the code is incorrect) 29

Question What will be the result of this

code?day = 2;switch (day){

case 1: console.log("Monday"); break;case 2: console.log("Tuesday"); break;case 3: console.log("Wednesday"); break;default: console.log("Error!"); break;

}

a) Monday

b) Tuesday

c) Wednesday

d) Error!

e) syntax error (the code is incorrect) 30

Question What will be the result of this

code?day = "2";switch (day){

case 1: console.log("Monday"); break;case 2: console.log("Tuesday"); break;case 3: console.log("Wednesday"); break;default: console.log("Error!"); break;

}

a) Monday

b) Tuesday

c) Wednesday

d) Error!

e) syntax error (the code is incorrect) 31

Question What will be the result of this

code?var day = "Wed";switch (day){

case "Mon": console.log("Monday"); break;case "Tue": console.log("Tuesday"); break;case "Wed": console.log("Wednesday"); break;default: console.log("Error!"); break;

}

a) MonTueErr

b) Mon

c) Tue

d) Err

e) syntax error (the code is incorrect)

32

Question What will be the result of this

code?var day = 1;switch (day){ case 1: console.log("Mon"); case 2: console.log("Tue"); default: console.log("Err");}

Arrays

34

Question

Which of the following is the correct way to declare an array in JavaScript?a)

b)

c)

d)

e)

var arr = new Array("0":1,"1":2,"1":3)var arr = new [1,2,3]

var arr = new ([1,2,3]);

var arr = new Array(1,2,3)

var arr = new Array;

35

Answer

Initialing an array in JavaScript can be done in three ways: Using new Array( elements):

Using new Array( initialLength):

Using array literals:

var arr = new Array(1,2,3,4,5);

var arr = new Array(10);

var arr = [1,2,3,4,5];

36

Question

What will the following script

result in?

a) An exception will be thrown

b) The second line won’t be executed

c) A pop-up box with text "undefined" will appear

d) A pop-up box with text "2" will appear

e) A pop-up box with text "0" will appear

var arr = new Array(2);alert(arr[0]);

37

Answer

The code initializes an array of 2 elements No element has a set value So all elements are "undefined" alert(undefined) will produce a pop-

up box with the text "undefined" The code is valid, so no exceptions will be thrown

38

Question

What will the following script

result in?

a) An exception will be thrown

b) A pop-up box with text "undefined" will appear

c) A pop-up box with text "7" will appear

d) A pop-up box with text "6" will appear

var arr = [1, 2, 7]arr[3] = 6;alert(arr[3]);

39

Answer

The code initializes an array with the elements 1, 2 and 7

Writing to index 3 causes expansion of the array Element at index 3 is set to 6 by the

script We "alert" the element at index 3

A pop-up box with the text "6" appears

40

Question

What will the following script

make the arr array look like?

a) won’t change

b) won’t change and an exception will be thrown

c) will be:

d) will be:

var arr = [1, 2, 7];var i = 0;for(i=6; i>0; i--);{arr[i] = i}

arrarrarrarr

[0, 2, 7][1, 1, 2, 3, 4, 5, 6]

41

Answer

There’s a semi-colon after the loop The only thing the loop changes is After the loop, is 0 (zero)

will set to{arr[i] = i}

i

arr[0]

0

i

42

Question

What will the following script result in?

a) A pop-up with the text "false" will appear

b) A pop-up with the text "true" will appear

c) A pop-up with the text "undefined" will appear

d) The code will stop execution when it reaches the third line

e) An exception will be thrown

var first = [1, 2, 7, 2, 5];var second = [1, 7, 5];var res = (first == second.join(",2,"))alert(res);

43

Answer

The join operation return a string from array By inserting ",2," between every

two sequential elements In this script, the resulting string is

"1,2,7,2,5" Comparing array to a string does a .toString() on the array .toString() on the array

results in "1,2,7,2,5" "1,2,7,2,5" == "1,2,7,2,5" returns true

second

first

44

Question

What will the following script print on the console?

a) undefined undefined undefined 1 2

b) 0 0 0 1 2

c) 1 1 0 0 0

d) 1 2 undefined undefined undefined

e) 1 2

var arr = new Array(3);arr.push(1); arr.push(2);for(var i = 0; i < arr.length; i++)

console.log(arr[i]);

45

Answer

The array is initialized with 3 undefined elements

The push operation places elements at the end of the array The last two elements become 1

and 2 The array length is 5

The final form of the array is:[undefined, undefined, undefined, 1, 2]

46

Question What will running the following

script result in?

a) An endless loop

b) The array will be

c) The array will be

d) The array will be

e) The array will be

f) The array will be

var arr = new Array(1, 2, 3, 4, 5);for(var i = 0; i < arr.length; i++){

arr.unshift(arr[i]);arr.splice(arr[i+1], 1);

}console.log(arr);

5,4,3,2,1,2,3,4,51,1,1,1,1,2,2,2,3,3,3,3,4,4,55,4,3,2,11

1,2,3,4,5

47

Answer

The array is initialized with 1, 2, 3, 4, 5

The script takes the current element Inserts copy in the beginning All previous elements move 1 index

forward Meaning former "current element" is

now at i+1

Splices 1 position at i+1 Meaning delete the former "current

element"

Repeats this 5 times (array doesn’t change size)

Finally, array is reversed (warning: very slow)

48

Question

What will running the following script result in?

a) An exception will be thrown

b) The code will stop execution after the second line

c) A pop-up with the text "2,22,7" will appear

d) A pop-up with the text "-1,2,7,22" will appear

e) A pop-up with the text "undefined" will appear

f) A pop-up with the text "-1,2,22,7" will appear

var arr = new Array(7, -1, 2, 22);arr.splice(arr.indexOf(arr.lastIndexOf(arr.length)), 1);arr.sort();alert(arr);

49

Answer The array is initialized with 7, -1, 2, 22

arr.length is 4 lastIndexOf(4) will return -1

(nothing found) arr.indexOf(-1) will return 1 (index of -1)

arr.splice(1, 1) will remove the element -1

arr.sort() will sort the array Using the string representations of

elements The resulting array contains 2,22,7

This will be shown in the pop-up

DOM Manipulation

51

Question

What will running the following script return?

a)Nothing, the script is invalid and won’t execute

b)Nothing and an exception will be thrown

c) null, because "#" is used in querySelector

d)The element with id="header" (if any)

e)The element with id="#header" (if any)

document.getElementById("#header");

52

Answer

getElementById will return the element with the id matching the string parameter Regardless of the contents of the

parameter i.e. symbols like '#' are just symbols,

not commands If there is no element with that id,

return null

53

Question

To which element will node point to after the following script (if all referenced elements exist) ?

a)Nothing, the script is invalid and won’t execute

b)nodec) node.parentNoded)node.firstChild.previousSiblinge)node.firstChild.lastChildf) node.parentNode.previousSiblin

g

node = node.firstChild.nextSibling.lastChild.parentNode.previousSibling.parentNode

54

Answer

We get to node.firstChild.nextSibling.lastChild Then we use .parentNode and thus

get back to node.firstChild.nextSibling

Then we use .previousSibling and get back to node.firstChild

Then we use .parentNode again and get back to node

So node = node

Question Which syntax could be used to create

the HTML code with JavaScript?

a)

b)

c)

d) e)

f)

g)

<h1>Heading</h1>

document.createElement("h1").appendChild("Heading");var h = document.createElement("h1");var t = document.createTextNode("Heading");h.appendChild(t);

var t = document.createTextNode("Heading");t = document.createTextNode("Heading");

document.createElement(h1).appendChild("Heading");var t = document.createTextNode("Heading");t.createElement("h1");

document.createElement("h1"). firstChild(createTextNode("Heading"));

document.createElement(h1). nodeValue(createTextNode("Heading"));

Question Which of the following can be used to

select the body node if you have following html code?

a) body = document.getElementsByTagName(body);

b) var body=document.getElementsByTagName("body");

c) var body=document.getElementById("p").parentNode

d) var body = document.getElementsById("body");

e) bodyElement = document.getElementByTagName[0];

f) body=document.getElementsByClassName(p)[0]. parentNode

<html><body id="body"> <p id="p" class="p"> </p></body></html>

JavaScript OOP

Question Which of the following is the

correct way to create a class in JavaScript?a)class Person{}

b)function Person(){}

c) class Person(){}

d)var Person as Class{}

Question What will happen when the following

code executes?

a) Selects all div elements with class "comment" and sets their background to red

b) Selects all HTML elements with class "comment" and sets their background to green

c) Selects all JS variables and makes them HTML elements

d) Selects all HTML elements with class "comment" and sets their background to red

e) Selects JavaScript elements of class "comment and sets their background to red

divs = document.getElementsByClassName("comment");for(var i in divs){ divs[i].style.background="#f00";}

Question

Which is TRUE for JavaScript?

a) JavaScript is extension to Java and is created for easier software development

b) JavaScript is a programming language, used in embed systems development

c) JavaScript is a programing language for web, desktop and mobile development

d) JavaScript is a programing language is platform dependent

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