Elance Javascript Test Answers 2015
·
JavaScript is ...
subjective
objective
evil
object based
var obj1 = {}; var obj2 = {}; What is the
value of (obj1 === obj2)
true
false
The loop isn't working. What's the problem?
<code> var foos = ['a', 'b', 'c' , 'd', 'e']; var bars = ['x', 'y', 'z'];
for (var i = 0; i < foos.length; i++) { var foo = foos[i]; for (var i = 0; i
< bars.length; i++) { var bar = bars[i]; /* some code using `bar` */ } }
</code>
The inner loop resets the outer for-loop, leaving
it a fixed position each time, causing an infinite loop (hint: no block scope).
The outer-loop finishes after the first iteration
due to a "bug" that unfortunately is part of the ECMAScript
specification.
There is no bug. The loop will run correctly.
Uncaught SyntaxError.
What does the following expression return? 1 +
5 + " bottles of milk";
"15 bottles of milk"
"6 bottles of milk"
undefined. An exception is thrown
"5 bottles of milk"
How do you create an object in JavaScript?
var obj = {};
function Foo() {} var obj = new Foo();
All of these work.
var obj = new Object();
What is the result of the following statement:
typeof "x";
"character"
"[object String]"
Throws error "ReferenceError: x is not
defined"
"string"
"undefined"
Primitive types are passed by :
Value
Pointer
Reference
Which is not a primitive data type in
JavaScript?
boolean
number
string
character
Which of these is a correct method to create a
new array?
var myArray = ();
var myArray = [];
var myArray = new Array[];
var myArray = {};
var myArray = array();
To what type are values converted internally
when evaluating a conditional statement?
positive
negative
integer
tinyint
boolean
Which of these is not a logical operator?
!
&
&&
||
What is the value of x? var a = false; var x =
a ? “A” : “B”;
undefined
true
"A"
"B"
false
Which of the following variable types does not
exist in JavaScript?
boolean
number
object
double
string
How do you write a conditional statement that
will *only* execute the contained code if variable x has a value 5 of type
*number*?
if (x == 5) { ... }
if x = 5 ...
if (x === 5) { ... }
if x = 5 then ...
Which event fires whenever a control loses
focus?
onclick
onmove
onblur
onchange
Which of the following invokes a user-defined
object constructor function?
var x = new myConstructor();
var x = create myConstructor();
myConstructor x = create myConstructor();
myConstructor x = new myConstructor();
The function call Math.ceil(3.5) returns:
Throws a MathError exception.
4
0
3
How is an object property referenced?
myObj(foo)
myObj->foo
myObj<foo>
myObj.foo
myObj[foo]
Which of these operators compares two
variables by value AND type?
===
None of these
==
=
How would one declare a string variable?
Any of these
var fName = "Mary";
var names = "7";
var fName = new String;
function foo(){ var tmp =
'one_two_three_four_five'; return tmp.replace(/_/g, '+'); } What does foo()
return?
one_two_three_four_five
_______________________
one+
one+two_three_four_five
one+two+three+four+five
USERNAME and userName
Represent the name of the same variable
Represent the name of different variables
Represent the name of different constants
Represent the name of the same constant
Which of these could be a correct way to
create an instance of Person?
var Person john = new Person('John', 'Doe', 50,
'blue');
var john = new Person('John', 'Doe', 50, 'blue');
new john = Person('John', 'Doe', 50, 'blue');
Person john = new Person('John', 'Doe', 50,
'blue');
Which is the correct way to write a JavaScript
array?
var names = {0: "Tim", 1:
"Kim", 2: "Jim"};
var names = {1: "Tim", 2:"Kim",
3:"Jim"};
var names = ["Tim","Kim","Jim"];
var names = array("Tim", "Kim",
"Jim");
Which of the following asserts that the
variables `A`, `B`, and `C` have unequal values?
A !== B || B !== C
A !== B & B !== C
A !== B && B !== C && A !== C
A !== B
The `else` statement is ___
Does not exist, in JavaScript `or` and `then` are
used to specify code to execute for the "false" case of the `if`
statement.
used inside of an `if` statement. To specify the
code that should execute if the `if` condition is no longer true.
used together with the `if` statement to specify
the code that should execute when the `if` condition is false.
The "if" statement is used to:
Deal with logic that should execute only when a
condition is false
Convert an integer value to a boolean
Create a loop that runs as long as a condition is
true
Deal with logic that should execute only when a
condition is true
String literals are written using:
Just single quotes: 'example'
Either double quotes or single quotes:
"example" and 'example'
Just double quotes: "example"
How to return the first value of this array?
var myArr = [1, 2, 3, 4, 5]; var myVal = ...
myArr[0];
myArr.pop();
myArr[1];
myArr.shift();
myArr.unshift();
How does a "while" loop start?
while i=(1 <> 10)
while i=1 to 10
while (i<=10)
while (i<=10;i++)
Properties of a RegExp object include:
source
ignoreCase
lastIndex
All of these
What is the value of the following expression:
8 % 3
5
2
24
Other/Error
Given the following code, what does myFunc()
return? var foo = 'foo'; var bar = 'bar'; function myFunc() { return foo + bar;
}
"foobar"
NaN
"undefinedundefined"
An error is thrown because of illegal out of scope
access.
"foo + bar"
Which symbol is not used in logical
operations?
||
%
&&
!
How do you round the number 7.25, to the
nearest whole number?
Math.round(7.25)
rnd(7.25)
round(7.25)
Math.rnd(7.25)
Which of these will throw a SyntaxError?
if (x == 1) { }
if (x = 1) { }
if (x ==== 1) { }
if (x === 1) { }
What is the correct JavaScript syntax to
insert a comment that can span multiple lines?
// This comment has mor than one line *//
/ This comment has more than one line /
// This comment has more than one line //
/* This comment has more than one line */
JavaScript supports dynamic typing, you can
assign different types of values to the same variable.
true
false
How do you define a function called
"fName"?
function fName: { }
func fName = function () {}
function fName() { }
new fName = { }
None of these
How do you check what the type of a value in
variable x is?
gettype(x);
x.__type;
Object.type(x);
typeof(x);
Which of the following is not a reserved word?
throw
void
program
return
Which keyboard character represents the
assignment operator?
!
?
#
:
=
Which of the following is a valid function
definition?
function myFunc(arg1,arg2) { }
func myFunc = (arg1 as string, arg2 as int) { }
function myFunc(arg1, arg2):
String concatenation...
is the splitting of a String into two or more
Strings
Is a complex String
Is the combination of two or more text Strings
Is an elemental String
What is the value of ("dog".length)?
4
3
2
What is the value of x? var a = "A";
var x = a.concat("B");
"B"
"A"
"AB"
["A", " B"];
Which is NOT a way to create a loop in
javascript?
for (...) { }
do { } while(...)
while (...) { }
repeat (...) { }
In an array object, what is the key of the
first value?
0
$
1
-1
100
Which statement loops through an array?
for (i < myArray.length; i++)
for (i = 0; i <= myArray.length;)
for (var i=0; i < myArray.length; i++)
Where do you use the "break"
statement?
To divide (or "break") a mathematical
value in half.
To add a value to an array.
To delete a (global) variable.
To terminate an Object statement.
To terminate a switch statement, loop, or labeled
block.
The var statement is used to:
Create a new local variable
Retrieve a variable descriptor
Declare a member of a class
Change a constant
What does the "break" statement do?
Cancels the current event.
Aborts the current function.
Aborts the current loop or switch statement.
Simulates a JavaScript crash.
What character ends a javascript statement?
An exclamation mark "!".
A semicolon ";".
A period ".".
A colon ":".
Which of the following primitive values exist
in JavaScript?
boolean
string
number
All of these
Are variable identifiers case-sensitive?
No
Yes
Which of the following declares a variable
with a value of string type?
var string myVar = "This is a string";
var myVar = "This is a string";
string myVar = "This is a string";
You use the Math.pow() method to:
Return any number
Return a number raised to the power of a second
number
Return a random value between 0 and 1
Return a variable value
What keyword is used to begin a conditional
statement?
when
how
if
condition
What character combination is used to create a
single line comment?
!!
--
$$
//
Java script start with......
Do_script
Start_script
<script>
<scr>
var a = '011'; parseInt(a); will return:
11
0
9
error
null === undefined
true
false
What is the value of the array myArr after
execution of the following code: var myArr = [1,2,3,4,5]; myArr.shift();
[1,2,3,4,5]
[]
[2,3,4,5]
[1,2,3,4]
What does isNaN() do?
Only returns true if the argument is not a number
Converts a non-numeric value to a number.
Throws an error if a conditional statement is
false.
Properties of objects may be accessed using...
the dot notation in JavaScript.
none of these
the redirect notation in JavaScript.
What keyword is used to define the alternative
path to take in a conditional statement?
or
else
altenative
next
What is the difference between a while loop
and a do...while loop?
The code inside a do...while loop will always be
executed at least once, even if the condition is false.
The code inside a while loop will always be
executed at least once, even if the condition is false.
There is no difference between them.
Which of these descriptors applies to
JavaScript?
Loosely typed, values of any type can be assigned
to any variable.
Strongly typed, variables are declared with a type,
and you can not assign another type to the variable.
What operator is used for string
concatenation?
.
+
All of these
&
(function( ) { var x = foo( ); function foo(
){ return "foobar" }; return x; })( ); What does this function
return?
TypeError: undefined is not a function
"foobar"
ReferenceError: foo is not defined
undefined
foo( )
Which of the following is a JavaScript
comment?
-- comment
<!-- comment -->
// comment
\\ comment
# comment
What is the difference between == and === ?
The == is used in comparison, and === is used in
value assignment.
The == operator converts both operands to the same
type, whereas === returns false for different types.
The === is deprecated, and now they are exactly the
same.
A for loop is written as such: "for
(first property; second property; third property) {...}" What does the
third property represent?
An action to take at the end of the current loop
cycle
A condition to check at the beginning of a loop
cycle
An action to take at the beginning of the loop
cycle
What is the value of a : var a = 3; var b = 2;
var c = a; var a=b=c=1;
3
true
1
false
2
Which of the following orders can be performed
with the Array prototype "sort()" callback?
Ascending alphabetical
Descending alphabetical
ASCII ordering
All of these
When an array index goes out of bounds, what
is returned?
undefined
An error to the browser
Moderate
the first or last value in the array
A default value, like 0
Which of the following is the equivalent of
the following. if (a) { x = b; } else { x = c; }
x = a : b ? c;
x = a ? b : c;
x = a ? b , c;
Which message does the following log to the
console? bar(); function bar() { console.log('bar'); }
undefined
TypeError
SyntaxErrror
"bar"
Which is the correct syntax to write array
literals in JavaScript?
var x =
["blank","blank","blank"];
var x = array("blank", "blank",
"blank”);
var x =
{"blank","blank","blank"};
var x = new
Array(1:"blank",2:"blank",3:"blank")
What is the value of x? var obj = {};
obj["function"] = 123; x = obj.function;
native Function constructor
123
undefined. Silent failure.
undefined. SyntaxError due to illegal position of a
reserved word
Which of the following operators can assign a
value to a variable?
All of these
=
%=
+=
In JavaScript, to call a function directly,
you use:
function_expression -> ( arguments_if_any )
function_expression { arguments_if_any }
arguments_if_any ( function_expression )
( arguments_if_any ) -> function_expression
function_expression ( arguments_if_any )
How do you assign object properties?
obj(age) = 25 OR obj.age = 25
obj["age"] = 25 OR obj.age = 25
obj.age = 25 OR obj(@"age") = 25
What is the value of x? var x = '1'+2+3;
6
15
"123"
The statement generates an error.
Which of the following is an Error object
constructor?
EvalError
All of these
Error
RangeError
var a = {1:'one',2:'two',3:'three'}; var b =
Object.keys(a); What's the value of b?
An array with all of the distinct keys from the obj
a
An obj with autowired getters and setters for it's
key/values
A serialized copy of the obj a
none of the above
How do you assign an anonymous function to a
variable?
var anon = new Function () { };
var anon = function() { };
var anon = func() { };
var anon = func({});
How do you find the number with the highest
value of x and y?
Math.max(x, y)
ceil(x, y)
max(x, y)
top(x, y)
Math.ceil(x, y)
What is the RegExp object constructor used
for?
Match text against regular expressions
Provides access to Windows registry express values
Regulates the expression of variables
Registers experienced functions with the DOM
Switches numerical notation to exponential
Which of these is not a JavaScript statement?
throw
None, these are all valid statements.
continue
break
var data =
["A", "B", "C", "D"];
data.unshift("X"); data.push("Y"); What does data look
like?
["A", "B", "C",
"X", "D", "Y"]
["X", "Y", "A",
"B", "C", "D"]
["X", "A", "B",
"C", "D", "Y"]
["A", "B", "C",
"D", "X", "Y"]
["Y", "A", "B",
"C", "D", "X"]
The _______ operator returns a string that
identifies the type of its operand.
TypeOf
typename
Type
typeof
getType
The "exploit" property:
Represents a variable
Is a very important property
Is obsolete
Does not exist in JavaScript
JavaScript is an implementation of the ______
language standard.
VBScript
ActionScript
ECMAScript
HTML
Which has the correct syntax of a ternary
operation?
var x = ( y === true ) { "true" :
"false" };
var x = y === true ? "true" :
"false";
var x = y === true : "true" ?
"false";
var x = ( y === true ) : "true" ?
"false";
What is the name of the String prototype that
appends the given string to the base string and returns the new string?
"x".combine("foo")
"x".match("foo")
"x".add("foo")
"x".concat("foo")
None of these does that and/or such method doesn't exist
in javascript!
What will calling the below test function log
to console? function test(){ console.log(a); var a = 'hello'; console.log(a); }
ReferenceError: a is not defined
ReferenceError: a is not defined, "hello"
"", "hello"
undefined, "hello"
Functions in javascript are always ..
in the global scope
loops
objects
operators
If a function doesn't explicitly use the
"return" operator, what will the return value be when the function is
invoked?
null
undefined
false
closure
NaN
Which of the following have special meanings
within the language syntax?
Variables
Literals
Reserved words
Identifiers
Given a variable named stringVar with a string
value, what does the following do? stringVar.toUpperCase();
Return a copy of stringVar with all letters in
uppercase
Return the number of characters in the stringVar
variable
Evaluate any string expression in stringVar
Alters stringVar, changes all letters to uppercase
How do you declare a function?
function doSomething() {}
all of these
function=doSomething() {}
function:doSomething() {}
Which of the following is a way to add a new
value to the end of an array?
arr[value] = length;
arr.length = value;
arr[arr.length] = value;
arr[arr.length()] = value;
Which of the following is the syntax for an
object literal (with no properties)?
nil;
[];
();
{};
object;
What are curly braces ("{" and
"}") used for?
Parsing JSON
Defining a class
Block declarations and object literals
Setting attributes
Invoking a function
What is the value of x? var x = 2 +
"2";
22
4
"22"
"4"
What is result of the following expression:
var a = "test"; console.log(!!a);
SyntaxError
false
true
undefined
Which of the following is not a method in the
"JSON" object according to the ECMAScript specification?
JSON.stringify
JSON.fromString
JSON.parse
What is the result? 0 == ""
Error: type mismatch
true
false
What is the value of c? var a = function(){
this.b = 1; } var b = function(){ var b = new a().b; return 5 + b; } var c =
b();
5
null
6
undefined
Error thrown when running the code
How can you concatenate multiple strings?
Both of these
'One' + 'Two' + 'Three'
'One'.concat('Two', 'Three')
When writing an object literal, what is used
to separate the properties from each other?
a semicolon ";"
a full-stop "."
a colon ":"
a comma ","
an underscore "_"
What is the result of the following statement:
0 == "";
Throws Error, invalid comparison
false
null
true
Every object is linked to a _________ object
from which it can inherit properties.
argument
sibling
parent
prototype
What does "2" + 3 + 4 evaluate to?
9
'27'
'234'
Consider this code: var x = ['Hello']; What
value will 'x[1]' return?
"Hello"
null
undefined
['Hello']
NULL
var x = "foo"; x = !!x; What is the
value of x?
"!!foo"
true
undefined
NaN
Which is an example of (only) an object
literal in Javascript?
var obj = { prop1: 'property 1', prop2: 'property
2' };
var obj = [ "property 1", "property
2" ]
var obj = [ {prop1: 'property 1', prop2:
'property2'} ]
var obj = new Object() { this.prop1 = 'property 1';
this.prop2 = 'property 2'; }
What is the value of `x` after the following?
var x = "hello"; (function() { x = "goodbye"; }());
undefined. A SyntaxError is thrown
"goodbye"
"hello"
Is there a value type for individual string
characters?
No, there is only type "string" for
characters.
Yes, accessing a character offset from a
(non-empty) string will yield a value of type "char".
split() is a method of which constructors'
prototype?
String.prototype
None of these
Number.prototype
Array.prototype
What is the value of x? function foo(y) { var
z = 10; z = 7; }; var x = foo("bar");
undefined
7
10
"bar"
null
Math.random() returns..
a random number between 0 and 1
a random number that can be any value
a random number between 0 and 100
a random number between 0 and 1000
How can you get the number of characters in a
string ?
"1234567".Length()
"1234567".Length
"1234567".getLength()
"1234567".length
"1234567".length()
What is the result of the following
expression? ({"foo": true}).foo;
undefined
4
false
SyntaxError
true
In the loop, "for (first clause; second
clause; third clause) { statements; }" What does the second clause
represent?
A condition to check at the beginning of each loop
cycle
Code to execute once, after the loop has ended
A condition to check at the end of each loop cycle
Code to execute once, before the loop starts
What will invoking `foo` return? function
foo() { var x = 10; x = 7; };
7
10
undefined
null
foo
The "this" keyword refers to ...
function currently being executed.
parent object that hosts the current function.
current execution context (could be any value).
Given the following code, what is the value of
x? var x = ['foo', 'bar']; x.length = 1;
[]
["foo"]
["bar"]
["foo", "bar', 1]
["foo", "bar"]
'&' Operator is _____
a bitwise operator
an assignment operator
an operator used in conditionals
a displacement bit operator
var x = Math.ceil(10.126); What is the value
of x?
An error, because it was called incorrectly
11
10
10.13
The length property of an Array object is
always:
equal to the highest index of that object
equal to the number of properties in that object
equal to the highest index of that object + 1
Which fact is true about the keyword
"default"?
It does not exist in JavaScript
It branches program logic based on the value of a
condition
It catches any case clauses not caught by case
statements within a switch statement
It sets up one variable to check against multiple
values
Infinity * null will return :
NaN
null
Infinity
What is the value of x after the following
statement? var x = 1 == '1';
false
undefined
true
'1'
1
What is the end value of myAddedVar with the
following code: var myVar = '5'; var myAddedVar = myVar + 10;
NaN
'510'
15
510
Nothing, the code will result in an error.
Which of the following types does NOT exist in
javascript?
number
boolean
object
integer
string
What does null, undefined, "string",
20, true and false have in common?
they are primitive values
they are objects
they are functions
they have the same instance properties
What is the value of x? var x = typeof new
String("abc");
object
string
undefined
var y = 3, x = y++; What is the value of x?
3
4
5
2
6
How do you read the first character in a
string?
data.charAt(0);
data.slice(1)
data.substr(0);
data.charAt(1);
data.substring(1);
What is the value of x? var x = typeof null;
"object"
"null"
null
undefined
var data = [1, 2, 3, 4, 5, 6]; data.shift();
What does data look like?
[undefined, 2, 3, 4, 5, 6]
[6, 1, 2, 3, 4, 5]
[2, 3, 4, 5, 6]
[undefined, 1, 2, 3, 4, 5]
[1, 2, 3, 4, 5]
What is the type of `null`, according to the
`typeof` operator?
"undefined"
"object"
"array"
"null"
How would you iterate over the following
object? var my_data = {a: 'Ape', b: 'Banana', c: 'Citronella'};
None of these. One can only iterate over arrays,
not objects.
foreach (my_data as key => value) {}
for (var key in my_data) {}
for (var i = 0; i < my_data.length; i++) {}
What character combination is used to alter
the order of operations by grouping expressions?
( )
[ ]
< >
{ }
What does this line do? variable++;
Returns a value 1 greater than "variable"
without changing its value
Returns an error to the browser
Increments the value of "variable" and
returns the new value
Adds the value of "variable" to itself
Increments the value of "variable" but
returns the previous value
Which Object method takes a `propertyName`
parameter and returns `true` if the object contains an uninherited property
with that key?
obj.exists('propertyName');
obj.hasProperty('propertyName');
obj.doesPropertyExist('propertyName');
obj.hasOwnProperty('propertyName');
obj.contains('propertyName');
var a = new Boolean(false); What is (typeof
a)?
'false'
'primitive'
'number'
'object'
'boolean'
What's the difference between the
"var" keyword and the new "let" keyword which appears in
ECMAScript 6 ?
The "let" declares a local value to a
block scope whereas the "var" defines a variable more globally
The "let" was introduced only to deal
with for() loops because it's faster than a "var" in that case
The "let" allows programmers to do
variables assignment by "destructuring"
The "let" is the new "var".
It's faster to create and initialize variables in the computer
Does NaN equal itself?
No, when trying to compare it against itself, an
exception is thrown.
Yes, just like 123 is equal to (==) 123, NaN is
equal to NaN.
No, NaN does not equal itself (== comparison would
return false).
What is the value of x after the following
code is executed? var x = 0; x = x++;
1
0
Which of these is not a built-in object
constructor?
Time
Date
RegExp
Array
What is the result? "" ?
"a" : "b"
""
Error: "" is not a boolean
"b"
"a"
Which of these will invoke a function?
function.exec(...)
function.invoke(...)
function.Apply(...)
function.Execute(...)
function.apply(...)
Given the following code: var myVar = '5'; var
myAddedVar = myVar + 10; What is the value of (myAddedVar.constructor ===
Number)?
true
NaN
Type Error
undefined
false
function b(x, y, a) { arguments[2] = 10;
alert(a); } b(1, 2, 3); What is alerted?
2
1
10
3
What is the right way to combine two arrays
into a new array? var a = ["a", "b", "c"]; var b
= ["d", "e", "f"];
var c = a.push() + b.push();
var c = a.join(b);
var c = a.concat(b);
None of these
Which String prototype method is capable of
removing a character from a string?
delete()
remove()
replace()
destroy()
What will happen in the console after
executing this code? if ("foo") { console.log("foo" ===
false); console.log("foo" === true); }
false true
TypeError : Cannot convert to boolean
NaN NaN
false false
What will the expression a === b return after
the following? var a = { "foo": "bar" }; var b = {
"foo": "bar" };
false
undefined
true
An exception is thrown.
A javascript variable prefixed with a $ is:
only valid within certain javascript libraries
still valid, but deprecated since Javascript 1.6
valid javascript syntax as any other character
invalid, a common bug introduced by developers
coming from PHP or Perl
What is the difference between using call()
and apply() to invoke a function with multiple arguments?
apply() is identical to call(), except apply()
requires an array as the second parameter
apply() is identical to call(), except call()
requires an array as the second parameter
apply() is exactly identical to call()
apply() is deprecated in favor of call()
You use the Math.tan( ) method to:
Return the tangent of an angle (in degrees)
Return the tangent of an angle (in gradients)
Return the tangent of an angle (in radians)
Does not exist in JavaScript
What would this code print out? if (new
Boolean(false)) console.log("True"); else
console.log("False");
True
False
Which two values are logged by the following
code? var x = 5; (function () { console.log(x); var x = 10; console.log(x);
}());
nothing. Throws ReferenceError: x is not defined
undefined 10
5 10
10 10
An (inner) function enjoys access to the
parameters and variables of all the functions it is nested in. This is called:
Prototypal inheritance
Lexical scoping
Assuming alert displays a string of its
argument: var a = 10; function example(){ alert(a); var a = 5; } example();
What will be shown if the preceding code is executed?
undefined
null
5
10
var foo = 'Global'; function fun() { log( foo
); var foo = 'Local'; log( foo ); } fun(); What the output of the above to
log()?
undefined Local
Global Local
Local Local
Global Global
Which are the different ways to affect the
"this" reference in a function?
Direct attribution, e.g. this = x;
Only by invoking a function with the
"new" keyword
Invoking a function with the "new"
keyword, invoking through the .call() method, invoking through the .apply()
method.
the "this" keyword is a global reference that
always has the same value.
Only by invoking through the .call() or .apply()
method.
Which of the following is NOT a valid way to
write a loop that will iterate over the values in the array in variable
"myArray"?
for (var i = 0, len = myArray.length; i < len;
i++) {}
for (var i = 0; i < myArray.length; i++) {}
var i = 0; for (; i < myArray.length; i++) {}
None of these, they are all valid
for (var i = 0; i < myArray.length; i += 1) {}
What is the difference between the two
declaration methods below? var functionOne = function() { /* some code */ }
function functionTwo() { /* some code */ }
functionTwo is defined in-place (until that line,
functionTwo is undefined), whereas functionOne is hosted to the top of the
scope and is available as a function throughout the scope.
No difference, they are treated the same way by the
javascript engine. Different syntax to do the same.
functionOne is defined in-place (until that line,
functionOne is undefined), whereas functionTwo is hoisted to the top of the scope
and is available as a function throughout the scope.
functionOne is not a correct way to define
functions
What is the output? var one; var two = null;
console.log(one == two, one === two);
true true
Error: one is not defined
false false
true false
false true
Math.Pi returns the mathematical constant of
Pi. What standard JavaScript method would truncate Math.Pi to 3.14 ?
Math.Round(Math.Pi)
Math.Pi.toPrecision(2)
Math.Pi.toString("D2")
Math.Pi.toFixed(2)
Which of the following assigned values of x
will cause (x == x) to return false?
NaN
0/0
All of the answers
Number("foo")
When reserved words are used as keys in object
literals they must be ______?
Prefixed with the @ operator
quoted
This is not possible in javascript
escaped
(function() { 'use strict'; foo =
"bar"; })();
It creates a variable named "foo" in the
global object (window)
It enables the JavaScript strict mode and creates a
variable named "foo" in the global object (window)
It doesn't do anything
It throws an error : foo is not defined
It kills your browser
What is the value of x.length after running
this code? x = ["foo"]; x.quux = "Hello"; x[1] =
"bar";
Error on last line: index out of bounds
Error on middle line: cannot add properties to Array
2
1
3
What is the result of: function foo() {
output( "biz " + bar() ); } bar(); var bar = function() { return
"baz"; }
biz bar
foo baz
baz biz
TypeError: Undefined is not a function
biz baz
What does the following return? Number(null);
0
undefined
1
null
Evaluate: "10" - (17).toString()
Throws Javascript error
-7
3
10125
What is the value of x? var x = typeof NaN;
"number"
"double"
"nan"
"integer"
"object"
true + true will return :
true
2
undefined
How does JavaScript interpret numeric
constants outside of strict mode?
As hexadecimal if they are preceded by a zero only
As octal if they are preceded by an underscore
As octal if they are preceded by a zero, and as
hexadecimal if they are preceded by a zero and "x"
None of these are correct
The expression (typeof NaN ===
"number") evaluates to:
false
true
Throws an Error
What is the value of x after the code below is
executed? var x = ""; function foo() { x += "foo "; } var
bar = function() { x += "bar "; }; foo(); var quux = bar = foo;
quux();
"foo foo "
"foo bar"
"foo bar "
"bar "
Object.keys(x)
Incorrect syntax for using Object.keys.
returns a key that can be used to unlock the object
after Object.freeze(x).
returns the enumerable properties of x as an array
of strings.
returns all properties of x as an array of strings,
including non-enumerable properties.
What will be in console after executing this
code: console.log(1 + '1' - 1);
1
'1'
'111'
10
What values will the output function be called
with, in the following code: var foo; var bar = { name: "baz", email:
"fiz@example.com", sendmail: function() { } }; for (foo in bar) {
output(foo); }
"baz", "fiz@example.com", null
"baz", "fiz@example.com",
undefined
"name", "email"
Type Error
"name", "email",
"sendmail"
var x = {}; var foo = function () { this.hello
= "Hi"; return this; }; x.bar = foo; What is the value of the
following code: x.bar().bar().hello;
TypeError: Cannot call method 'bar' of undefined
"Hi"
"function () { this.hello = "Hi";
return this; }"
TypeError: Object -- has no method 'bar'
undefined
How can you remove an element from an array
and replace it with a new one ?
array.overwrite(...)
array.splice(...)
array.switch(...)
array.split(...)
array.replace(...)
Which of the following is not a reserved word
in the language?
and
while
debugger
instanceof
Which operator has highest precedence?
*
+
-
^
Which of the following String prototype method
takes a regular expression?
search()
indexOf()
charCodeAt()
All of these
Consider: var x = ['a', 'b', 'c']; Which line
of code will remove the first element of the array, resulting in x being equal
to ['b', 'c']?
x.unshift(0);
x.pop();
x.splice(0);
x.splice(0, 1);
What is the value of x? var x = 10/0;
NaN
0
Infinity
Runtime exception
What will: typeof typeof(null) return?
string
null
empty
Number
error
What will the console log when running this
code? Function.prototype.a = 1; var a = new Function(); a.prototype.a = 2; var
c = new a(); console.log(a.a , c.a);
1 1
Error thrown when running the code
2 1
2 2
1 2
What will be printed to the console as a
result of this code? var printName = function() { console.log('Matt');
printName = function() { console.log('James'); }; }; var copy = printName;
printName(); copy();
James Matt
Matt James
James James
Matt Matt
What will be the result of this expression:
void 0
undefined
null
TypeError
SyntaxError
Whats the output of the below : for(var i = 0;
i < 10;i++){ setTimeout(function(){console.log(i) }, 10)}
0 1 2 3 4 5 6 7 8 9
10 10 10 10 10 10 10 10 10 10
10 10 10 10 10 10 10 10 10
Error
What is the value of x? var z = [typeof z,
typeof y][0]; var x = typeof typeof z;
"array"
"string"
"object"
"undefined"
Evaluate: undefined + 2
2
undefined
NaN
Type Error
Evaluate: new Boolean(new
Boolean(false)).valueOf()
true
(Instance of object Boolean with valueOf false)
undefined
Type Error
false
console.log( typeof [1,2] ) will print out:
array
object
string
number
undefined
function Question() { this.answered = false; }
Question.prototype.rightAnswer = 5; console.log( new Question().rightAnswer,
Question.rightAnswer ); What gets printed to the console?
5 undefined
undefined undefined
undefined 5
5 5
After the following code: var a = function(){
this.b = 1; this.deleteMe = function(){ delete this; } }; var c = new a();
c.deleteMe(); What is the value of (String(c))?
Error thrown
(empty)
null
[object Object]
undefined
function foo(){ var tmp =
'one_two_three_four_five'; return tmp.replace('_', '+'); } What does foo()
return?
one+two_three_four_five
one_two_three_four_five
one+
one+two+three+four+five
one_
What will we see in the console after the
following code run: var a = 'Bolt'; function f() { if (!a) { var a = 'Nut'; }
console.log(a); } f(); console.log(a);
'Nut' and 'Nut'
'Bolt' and 'Bolt'
'Nut' then 'Bolt'
'Bolt' then 'Nut'
What will be the value of result? function
foo(bar) { return bar ? bar == foo : foo(foo); } var result = foo();
Function won't work due to incorrect syntax
Function will end up in infinite loop
Value will be null
true
false
What are the values of x and y after the invocation
of `foo` in following? var x = "I am global x"; var y = "I am
global y"; function foo() { var y = x = "Hello from foo"; }
foo();
x = "I am global x"; y = "I am
global y";
The function throws a SyntaxError
x = "Hello from foo"; y = "I am
global y";
x = "Hello from foo"; y = "Hello
from foo";
Which of these will create a copy of an array
such that changes to the old array will not be reflected in the new array?
var newArray = oldArray;
var newArray = new Array(oldArray);
var newArray = oldArray.slice(0);
var newArray = [oldArray];
Given the following code, what will
myFunction(123, false, "test") return? function myFunction(param) {
return arguments[1] || param; }
false
"test"
123
true
undefined
var q = null; q++; What is q?
Type Error
null
NaN
1
Math.min() < Math.max(); will return
undefined
false
null
true
var x = { foo: "A" };
x.constructor.prototype.foo = "B"; var y = {}; console.log(x.foo);
console.log(y.foo); Which two values will be logged?
"A" "A"
"A" "B"
"B" "B"
"B" undefined
"A" undefined
What is the output of the following? var x =
1; console.log(x++ + ++x + x);
3
4
7
6
What is the value of x after the following
code is run? var obj = { 0: 'who', 1: 'what', 2: 'idontknow'}; var x = 1 in
obj;
"what"
true
undefined
"who"
Nothing, the code throws a syntax error
What does Math.random() do?
Returns a random number more than 0 and less than
1.
Randomly put numbers in descending and ascending
order
Randomly selects a number 1-10.
Returns a random number more than 0 up to and
including 1.
Returns a random number from and including 0 to
less than 1.
What is the value of mike after this code is
run? function Person(name, age) { this.name = name; this.age = parseInt(age,
10); } var mike = Person('Mike', '25');
{ name: 'Mike', age: '25' }
This code won't run. It throws a SyntaxError.
null
undefined
{ name: 'Mike', age: 25 }
"bar".split().length returns:
3
1
2
throws an error
What value is passed to function
"foo" as first argument? foo( +"5" );
5
0
NaN
"5"
"05"
console.log(1 + +"2" +
"2")
Error
122
"122"
32
What will this code produce: +new Date()
Unix timestamp in milliseconds (UTC timezone)
The Unix epoch (1970-01-01 00:00:00)
Unix timestamp in milliseconds (Local timezone)
A SyntaxError
function foo() { this = "foo"; } var
a = foo(); What will the preceding code produce?
ReferenceError: Invalid left-hand side in
assignment
"undefined"
SyntaxError: Unexpected token
undefined
"foo"
What is the value of a after executing the
following: var a = [1, 2, 3]; a.splice(1, 2, 3);
[1, 2, 3, 1, 2, 3]
[ ]
[1, 2, 3, 2, 3]
[1, 3]
[1, 2, 3]
Evaluate the following expression: ~-(2 +
"2")
22
21
23
true
-22
Math.log(x) returns:
Logarithm base 2 of x.
Logarithm base 8 of x.
Logarithm base 10 of x.
Logarithm base e (Euler's number) of x.
Object("s") instanceof String ===
"s" instanceof String
false
true
What will the following code, when evaluated,
do? var void = function () {};
Create a local variable named "void" but
stays undefined due to a SyntaxError.
Throw a SyntaxError
Assign an anonymous function to variable named
"void"
Which of the following expressions evaluates
to false?
new Boolean('false') == false
new Boolean(0) == 0
new Boolean('true') == true
new Boolean(1) == 1
They're all evaluate to true
What is the value of c? var a = function(){
this.b = 1; } var b = function(){ this.b = new a().b; return 5; } var c = b() +
new b();
1
6
[object]
Error thrown when running the code
5
Which of the following Array prototype method
actually modifies the array it's been called on?
concat()
slice()
all of them
splice()
What does the following return? Math.max();
null
-Infinity
Infinity
0
var obj1 = {}; var obj2 = {}; What are the
value of the below: !!(obj1 && obj2) (obj1 && obj2)
false true
true {}
true fasle
{} false
What is the value of "x" after the
following code runs? var x; x++;
1
Throws a TypeError on the "x++;"
statement
0
NaN
undefined
In JavaScript (ES5) Oriented-Object
Programming, is it possible to have a member property of a constructor function
to a private state ?
No, because JavaScript is not really
Object-Oriented and doesn't have the `private` and `static` keywords like
others OOP languages
Yes, by creating a local variable inside your
constructor. Moreover, this will allow the methods created in the prototype to
access this "private-like" property
Yes, by using the `private` keyword before
declaring your member property
No, it's actually not possible because every member
you will define inside the constructor will be accessible from the outside
Yes, by nesting your constructor function into a
IIFE and creating local variables in it
String values have a "length" property.
Why is this property not included in a for-in loop over a string object? var
prop, str; str = 'example'; /* str.length === 7 */ for ( prop in str) {}
Because the "length" property is only in
the String prototype, it is not an own property of string objects, and as such
is not included in a for-in loop.
Because the "length" property has
internal [[Enumerable]] set to false.
Because the "length" property isn't a
real property (defined and set through get/set accessors). Properties with accessors
are not included in for-in loops.
Which are the different value types in
JavaScript?
boolean, integer, float, string, array, object and
null
boolean, number, string, function, object and
undefined
boolean, number, date, regexp, array and object
boolean, number, string, function, object, null and
undefined
What is the value of x? var a =
"abc"; var x = a instanceof String;
true
false
What's the correct syntax for creating a Date
object for January 10, 1998?
new Date(1, 10, 1998);
new Date(0, 10, 1998);
new Date(1998, 0, 10);
new Date(1998, 1, 10);
Evaluate: ![]+[]
true
false
undefined
'false'
Syntax Error
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