JAVASCRIPT

Question 1

Who originally developed JS?

Answer 1

Branden Eich.

Question 2

What was JS originally called?

Answer 2

LiveScript

Question 3

When was JS named JS? Why then?

Answer 3

LiveScript was renamed JavaScript in 1995, as it became a joint venture of Netscape and Sun.

Question 4

Who standardized JS as ECMA-262?

Answer 4

The European Computer Manufacturers Association.

Question 5

Is JS statically or dynamically typed?

Answer 5

Dynamically.

Question 6

JS is solely a client side language.

Answer 6

False - it may be used server side as well.

Question 7

Is JS case sensitive?

Answer 7

Yes.

Question 8

What’s a synonym for dynamic typing?

Answer 8

Loose typing.

Question 9

What is the root object in JS?

Answer 9

Object

Question 10

What type of inheritance does JS exhibit?

Answer 10

Prototypal inheritance.

Question 11

Is there polymorphism in JS?

Answer 11

No.

Question 12

A web server is needed for JS.

Answer 12

False.

Question 13

Write the html to import an external script.js file.

Question 14

How can JS code be embedded into html?

Answer 14

<script>
...
</script>

Question 15

What are the ways to write comments in JS?

Answer 15

// …
/* … */

Question 16

What JS object provides functions such as floor, round, max, min, etc?

Answer 16

Math

Question 17

What are the 5 JS primitive types?

Answer 17

Number, String, Boolean, Undefined and Null.

Question 18

Do the null type and the undefined type have several possible values?

Answer 18

No.

Question 19

What is returned by an arithmetic operation that creates overflow?

Answer 19

NaN

Question 20

What does (NaN == NaN) return?

Answer 20

False.

Question 21

How should you check for NaN values?

Answer 21

isNaN(x)

Question 22

What are the 4 ways of declaring a JS variable?

Answer 22

using var, let, const, or using nothing.

Question 23

What operator coerces strings into numbers, and numbers into strings depending on the context?

Answer 23

+

Question 24

List 2 ways of explicitly converting a number into a string.

Answer 24

Using the String constructor, or using a number’s toString() method.

Question 25

List 2 ways of explicitly converting a string to a number.

Answer 25

Using the Number constructor, or using parseInt() / parseFloat() functions.

Question 26

What does the following print?
console.log(1 + 2 + “bird”);

Answer 26

3bird

Question 27

When does the + operator execute numeric addition, rather than concatenation?

Answer 27

Only when both operands are numbers.

Question 28

What is the result of ‘$’ + 3 + 4 ?

Answer 28

$34
(left to right execution)

Question 29

When does < or > execute a number comparison?

Answer 29

When both operands are numbers, or if one is a number and the other can be converted to a number.

Question 30

When is the result of a < or > comparison always false?

Answer 30

When one operand is a number, the other isn’t and can’t be converted to a number.

Question 31

What is the result of “11” < “2”?

Answer 31

True, because a string comparison is performed if both operands are strings.

Question 32

What is the result of the following?
11 < 2+ “birds”

Answer 32

False, since the RHS becomes “2birds” which can’t be converted to a number in JS.

Question 33

What is the result of the following?
‘$’ + 3 < 4

Answer 33

False - can’t convert ‘$3’ to a number.

Question 34

When is * a number multiply?

Answer 34

If both operands are numbers, or both can be converted to a
number.

Question 35

What is the result of a multiplication (*) wherein one of the operands cannot be converted to a number?

Answer 35

NaN

Question 36

What is the result of the following?
‘$’*3 < 4

Answer 36

False.

Question 37

Is there a character type in JS?

Answer 37

No.

Question 38

How many bits are each character in a JS string?

Answer 38

16

Question 39

How can characters be represented in JS?

Answer 39

As strings with a length of 1.

Question 40

Are strings immutable in JS?

Answer 40

Yes.

Question 41

The == operator can be used to check for value equality between 2 strings in JS.

Answer 41

True.

Question 42

Do string literals use single or double quotes in JS?

Answer 42

Either.

Question 43

How can you obtain the length of a string object?

Answer 43

str.length

Question 44

What is the difference between ‘String(val)’ and new ‘String(val)’ ?

Answer 44

String(val) returns a string,
new String(val) returns an object.

Question 45

What does the following code print?
var a = “123”;
var b = “123”;
document.write(a==b);

Answer 45

true

Question 46

What method can return the character at a specified index, x, of a string, str?

Answer 46

str.charAt(x)

Question 47

What method (not operator) can join two strings, s1 & s2, into a single string?

Answer 47

s1.concat(s2)

Question 48

What method returns the index position of some character/substring str2 within str1?

Answer 48

str1.indexOf(str2)

Question 49

What method returns the index position of some character/substring str2 within str1, and searches right to left?

Answer 49

str1.lastIndexOf(str2)

Question 50

What method compiles all instances of a string (or regex), x, found within a string str, into an array it then returns?

Answer 50

str.match(x)

Question 51

What method can replace all instances of str2 with str3, within str1?

Answer 51

str1.replace(str2, str3)

Question 52

Does .replace() change the original string?

Answer 52

No, it returns a new one with the changes made.

Question 53

What does the str.search(x) method do?

Answer 53

It returns the index (position) of the first match of x within str.

Question 54

What does .search() return if no matches are found?

Answer 54

.search() returns -1.

Question 55

What JS method returns a substring of str, between indices i1 and up to (but not including) i2?

Answer 55

str.slice(i1, i2)

Question 56

What does str.split(“,”) do?

Answer 56

It splits str at its commas and returns an array of the resulting substrings.

Question 57

What method behaves almost exactly str.slice(i1, i2)?

Answer 57

.substring()

Question 58

Do the JS methods str.toUpperCase() and str.toLowerCase() put all characters of str to upper/lower case, or only the first?

Answer 58

All.

Question 59

In JS, what non-Boolean equate to Boolean false? (6)

Answer 59

0, -0, “”, NaN, undefined, null.

Question 60

In JS, “0” equates to what Boolean value?

Answer 60

True.

Question 61

How can you explicitly convert a non Boolean to a Boolean value?

Answer 61

Boolean(val)

Question 62

What does the following return?
Boolean(“false”);

Answer 62

true

Question 63

What does the JS Date object’s .getTime() method return?

Answer 63

The number of milliseconds since January 1, 1970.

Question 64

What JS object represents the model for the browser’s display window?

Answer 64

The Window object.

Question 65

What’s the difference between the JS alert(msg) and confirm(msg) functions?

Answer 65

The confirm popup has an additional “cancel” button.

Question 66

What does the JS prompt() function do?

Answer 66

Creates a popup window capable of accepting input.

Question 67

What is the purpose of the optional second parameter of the prompt() method?

Answer 67

The optional second parameter specifies the default text within the input section of the popup.

Question 68

What’s the difference between == / != and === / !== ?

Answer 68

=== / !== don’t do type coercion.

Question 69

what does “123” == “123” return?

Answer 69

true

Question 70

What does (3 !== “3”) return?

Answer 70

true

Question 71

What is the output of the following?
var a = new String(“123”);
var b = new String(“123”);
document.write(a==b);

Answer 71

false, due to the (double) use of the new operator.

Question 72

What is the output of the following?
var a = String(“123”);
var b = new String(“123”);
document.write(a==b);

Answer 72

true

Question 73

&& and || always return Boolean values.

Answer 73

False - && returns the second operand if the first is truthy (else it returns the first) and || returns the first operand if it is truthy (else it returns the second).

Question 74

! always returns a Boolean value.

Answer 74

True.

Question 75

Explicitly convert a value to true or false without using Boolean(val).

Answer 75

!!val

Question 76

How many bitwise operators are there in JS? List them.

Answer 76

6 - &, |, ~, ^, «,&raquo_space;

Question 77

What does the & operator do?

Answer 77

& ANDs the binary representations of its operands.

Question 78

What does the | operator do?

Answer 78

It ORs the binary representations of its operands.

ORs

Question 79

What does the ~ operator do?

Answer 79

It negates (flips) the binary representation of its operand.

Question 80

What does the ^ operator do?

Answer 80

It XORs the binary representations of its operands.

Question 81

What does the &laquo_space;operator do?

Answer 81

It bit-shifts the binary representation of its first operand by n bits to the left, where n is the second operand.

Question 82

What does the&raquo_space; operator do?

Answer 82

It bit-shifts the binary representation of its first operand by n bits to the right, where n is the second operand.

Question 83

The default case must be the last case in a JS switch block.

Answer 83

False.

Question 84

Along with while and for loops, do-while loops also exist in JS.

Answer 84

True.

Question 85

When was the let keyword introduced?

Answer 85

In 2015.

Question 86

Can variables defined with let be redeclared?

Answer 86

No.

Question 87

Can variables defined with let be used before declaration?

Answer 87

No.

Question 88

What is the scope of a variable defined with let?

Answer 88

Variables defined with let have block scope.

Question 89

Can variables defined with var be redeclared?

Answer 89

Yes.

Question 90

Can variables defined with var be used before declaration?

Answer 90

Yes.

Question 91

What is the scope of variables defined with const?

Answer 91

Variables defined with const have block scope.

Question 92

What is the scope of variables declared with var?

Answer 92

Either the enclosing function and functions declared within it, or global if declared outside any function.

Question 93

Variables with const cannot be redefined, but they can be redeclared.

Answer 93

False - they also can’t be redeclared.

Question 94

What is the scope of variables defined with const?

Answer 94

Variables defined with const have block scope.

Question 95

What is the output of the following code?
var name = “APPLE”;
{ var name = “BANANA”;
console.log(name); }
console.log(name);

Answer 95

BANANA
APPLE

Question 96

What will be the value of a variable used prior to declaration?

Answer 96

Undefined.

Question 97

What will happen if I remove the second line?
alert(“0-“+scope);
var scope = “global”;

Answer 97

An error is produced.

Question 98

What will be the output of the following?
console.log(x);
var x = “APPLE”;
function checkloc() {
console.log(x);
var x;
}
checkloc();

Answer 98

undefined
undefined

Question 99

What will be the output of the following?
console.log(x);
var x = “APPLE”;
function checkloc() {
var x;
console.log(x);
}
checkloc();

Answer 99

undefined
undefined

Question 100

What will be the output of the following?
console.log(x);
var x = “APPLE”;
function checkloc() {
console.log(x);
}
checkloc();

Answer 100

undefined
APPLE

Question 101

What is the output of the following?
checkloc();
console.log(x);
function checkloc() {
x = “APPLE”;
console.log(x);
}

Answer 101

APPLE
APPLE

(so long as the function is called first, x becomes global)

Question 102

What is the output of the following?
checkloc();
console.log(x);
function checkloc() {
var x = “APPLE”;
console.log(x);
}

Answer 102

Error!

Question 103

What is the least ambiguous way of accessing a global variable, x, from within a function definition?

Answer 103

window.x

Question 104

The following is valid JS code:
const PI;

Answer 104

False, const variables must be assigned a value at
declaration.

Question 105

Create a new object, C1, and give it two attributes, a1 & a2.

Answer 105

var C1 = new Object();
C1.a1 = “A”;
C1.a2 = “B”;

Question 106

How would delete an attribute, a1, from an object C1?

Answer 106

delete C1.a1;

Question 107

Can object properties can be accessed using array notation?
ex. var p1Copy = myObject[“p1”];

Answer 107

Yes.

Question 108

Create a new object, C1, and give it two attributes, a1 & a2, using the JSON way.

Answer 108

var C1 = { a1: “A”, a2: “B” };

Question 109

Can you use const to declare objects?

Answer 109

Yes.

Question 110

Can you change/add properties to objects declared with const?

Answer 110

Yes - you just can’t reassign the name being used for that object.

Question 111

Write a loop that would allow you to traverse the properties of an object, C1.

Answer 111

for (var prop in C1) { … }

Question 112

Write a conditional statement that checks for the existence of property a1 in object C1.

Answer 112

‘a1’ in C1

Question 113

What does the instanceof operator do?

Answer 113

Returns true if the LHS variable holds an instance of the a specific object class, which is specified by the constructor for that class on the RHS.

Question 114

What is the output of the following?
var myCar = {make:”ford”, model: “Contour SVT”};
console.log(myCar instanceof myCar);

Answer 114

ERROR - the RHS “myCar” is an instance, not the name of a defined class.

Question 115

You can’t add/change elements of an array declared with const.

Answer 115

False - you simply can’t reassign the name used for it.

Question 116

What is the output of the following?
var s1 = new String(“A”);
var s2 = “A”;
console.log(s1 instanceof String);
console.log(s2 instanceof String);

Answer 116

true
false

(Strings are necessarily objects)

Question 117

What is the output of the following?
var l1 = new Array(1, 2, 3);
var l2 = [1, 2, 3];
console.log(l1 instanceof Array);
console.log(l2 instanceof Array);

Answer 117

true
true

(Arrays are necessarily objects)

Question 118

What is returned by a function with no ‘return’?

Answer 118

undefined

Question 119

Are functions objects in JS?

Answer 119

Yes.

Question 120

What is returned by a function with ‘return’, but no return parameter.

Answer 120

undefined

Question 121

Missing/excess function parameters cause JS to crash.

Answer 121

False - missing parameters are given the value ‘undefined’ and excess parameters may simply be ignored.

Question 122

Can functions be passed as parameters in JS?

Answer 122

Yes.

Question 123

Will arr.sort(f) sort arr (an array of numbers) in increasing or decreasing order?
function f(a, b) {
return a - b;
}

Answer 123

Increasing order.

Question 124

Does the default sort() (no parameters) work on arrays of numbers/strings?

Answer 124

Strings, yes, but not numbers.

Question 125

A function passed as parameter to sort will either return a number less than, equal to, or greater than 0. How are the two parameters to the passed function, a & b treated depending on the outcome?

Answer 125

If a number less than 0 is returned, a is sorted to a lower index than b. If 0 is returned, a and b are considered equal. If a number greater than 0 is returned, a is sorted to a higher index than b.

Question 126

Define a constructor for an object, C1, which has 2 attributes, a1 & a2.

Answer 126

function C1(a1, a2) {
this.a1 = a1;
this.a2 = a2;
}

Question 127

Write a function that writes the attributes, a1 & a2, of an object C1 to the html document.

Answer 127

function displayC1() {
document.write(this.a1, this.a2);
}

Question 128

How can you make changes to the template of an object?

Answer 128

Using Object.prototype

Question 129

Do changes to Object.prototype affect all instances of that object?

Answer 129

Yes.

Question 130

Can you put functions into an object’s prototype?

Answer 130

Yes.

Question 131

In JS, prototypes are used to build longer chains of …?

Answer 131

Inheritance.

Question 132

new RegExp() is a valid built-in JS constructor.

Answer 132

True.

Question 133

new Function() is a valid built-in JS constructor.

Answer 133

True.

Question 134

Can you define JS classes … SLIDE 30, 4.4

Question 135

When defining a class in the following format (in JS), how would you define the constructor?
class C1 { … }

Answer 135

constructor(a1, a2) {
this.a1 = a1;
this.a2 = a2;
}

Question 136

Assume class C1 { … } has been defined with 2 string attributes, a1 & a2. How would you then create an instance of it?

Answer 136

const c1 = new C1(“hi”, “bye”);

Question 137

What are the 2 primary pattern matching methods, and what do they return?

Answer 137

str.search(reg) which returns the index of the matching string (or -1) and str.match(reg) which returns the matching string (or an array of matches).

Question 138

When does .match() return an array, rather than a string?

Answer 138

When the passed pattern has the global flag ‘/g’.

Question 139

Can we return all substrings that match a specified regex, without including the global flag in that regex?

Answer 139

Yes, using the .matchAll() method rather than .match().
(this returns an iterator, and not an array)

Question 140

How many matches does the following return?
‘abc’.match(/[abc]/g);

Answer 140

3

Question 141

How many matches does the following return?
‘abc’.match(/[a-b]/g);

Answer 141

2

Question 142

How many matches does the following return?
‘abc’.match(/abc/g);

Answer 142

1

Question 143

How many matches does the following return?
‘abc’.match(/[^abc]/g);

Answer 143

0
(^ is negation within [brackets])

Question 144

How many matches does the following return?
‘abc’.match(/^[abc]/g);

Answer 144

1
(^ implies left-end search outside [brackets])

Question 145

What will the following regex match agaisnt?
/./

Answer 145

Any single character, except newline or line terminator.

Question 146

Write the the long form of the following regex.
/\d/

Answer 146

/[0-9]/

Question 147

Write the the long form of the following regex.
/\D/

Answer 147

/[^0-9]/

Question 148

Write the the long form of the following regex.
/\w/

Answer 148

/[A-Za-z_0-9]/
(underscores are also valid)

Question 149

Write the the long form of the following regex.
/\W/

Answer 149

/[^A-Za-z_0-9]/

Question 150

Write the the long form of the following regex.
/\s/

Answer 150

/[ \r\t\n\f]/
(any 1 of 5 possible whitespace characters)

Question 151

Write the the long form of the following regex.
/\S/

Answer 151

/[^ \r\t\n\f]/

Question 152

What does the following regex quantifier do?
{4}

Answer 152

Exactly 4 repetitions of the previous character.

Question 153

What does the following regex quantifier do?
{4,}

Answer 153

At least 4 repetitions of the previous character.

Question 154

What does the following regex quantifier do?
{4, 6}

Answer 154

At least 4 (but no more than 6) repetitions of the previous character.

Question 155

Will the following return a match?
‘aaaa’.match(/a{2,3}/);

Answer 155

Yes - aaa

Question 156

Will the following return a match?
‘aaaa’.match(/a{2,}/);

Answer 156

Yes - aaaa

Question 157

What’s the difference between the following regex quantifiers?
*, +, ?

Answer 157

• is zero or more repetitions,
  + is one or more repetitions,
  ? is zero or one repetitions.

Question 158

What are the two regex anchors?

Answer 158

^ and $

Question 159

How many matches does the following return?
‘abc’.match(/[abc]$/g);

Answer 159

1

Question 160

How many matches does the following return?
‘abc’.match(/^[abc]$/g);

Answer 160

0
(just ‘a’/’b’/’c’ would’ve returned 1 match)

Question 161

What value does the following return?
‘abc abc’.search(/[^abc]/)

Answer 161

3

Question 162

What are the 3 common pattern modifiers?

Answer 162

i, g, m.

Question 163

What does the i regex modifier do?

Answer 163

i ignores the case of letters.

Question 164

What does the g regex modifier do?

Answer 164

Returns all matches, instead of just the first.

Question 165

What does the m regex modifier do?

Answer 165

Regex applies to mulitple lines.

Question 166

How do the ^ and $ anchors behave in multiline mode? (m)

Answer 166

^ matches beginning of line or beginning of string, and $ matches end of line or end of string.

Question 167

What method allows me to replace instances of a regex (reg) match in a string, str1, with a new string, str2.

Answer 167

str1.replace(reg, str2);
(also accepts strings in place of the regex).

Question 168

What method returns a string, str1, as an array split at a specified regex, reg?

Answer 168

str1.split(reg);
(also accepts strings, and an optional second parameter to limit the length of the array).

Question 169

5.1 slide 1

Answer 169

ok

Question 170

How many versions of DOM is there?

Answer 170

4 (DOM 0 - DOM 3)

Question 171

When was the latest DOM standard (DOM 3) approved?

Answer 171

2004

Question 172

What does DOM stand for?

Answer 172

Document Object Model

Question 173

JS’s Window object has what property?

Answer 173

document - a reference to the Document object that the window displays.

Question 174

document.forms[0].elements[0] is a valid way of accessing the first element of the html document’s first form.

Answer 174

True - although it is better to use the name attribute.

Question 175

What form element(s) have an implicit array?

Answer 175

Checkboxes and radio buttons.

Question 176

What name is given to the process of connecting an event handler to an event?

Answer 176

Registration

Question 177

Event handlers can only be assigned directly in the html as an attribute.

Answer 177

False - you may also assign the handler as a property in JS.

Question 178

What are the 3 ways in which an HTML element can get focus?

Answer 178

When the user clicks on it, when the user tabs to it, or when it is the target of the focus() method.

Question 179

When is the ‘load’ event triggered?

Answer 179

When the loading of a document is completed.

Question 180

What is a disadvantage of registering handlers in JS?

Answer 180

There is no way to use parameters.

Question 181

What are 2 advantages to registering handlers in JS?

Answer 181

It is good to keep HTML and JS separate, and the handler could be changed during use.

Question 182

What are the 6 possible values of position?

Answer 182

absolute, relative, static, fixed, inherit and sticky.

Question 183

What is the default value of the position property?

Answer 183

static

Question 184

Are statically positioned elements affected by the top/bottom/left/right properties?

Answer 184

No.

Question 185

How do relatively positioned elements behave?

Answer 185

They are positioned relative to their normal position using the top/right/bottom/left properties.

Question 186

How do fixed positioned elements behave?

Answer 186

They are positioned relative to the viewport (they don’t move when scrolling) using the top/bottom/left/right properties.

Question 187

How do absolutely positioned elements behave?

Answer 187

They are positioned relative to the nearest positioned ancestor (ancestor that is positioned relatively) using the top/bottom/left/right properties.

Question 188

How do sticky positioned elements behave?

Answer 188

These toggle between relative and fixed, depending on the scroll position.

Question 189

Which position value results in an element that can’t be moved using JS?

Answer 189

Static.

Question 190

Is space on the page still taken up by an element who’s visibility property is set to “hidden”?

Answer 190

Yes.

Question 191

What’s the default value of the visibility property?

Answer 191

visible

Question 192

How could you make an element invisible and not take any space? (as if it weren’t there)

Answer 192

Set it’s display property to none.

Question 193

Write the code to change a link’s colour once the moues hovers over it (the colour must not change back). Use an event.

Answer 193

onmouseover = “this.style.color = ‘blue’;”

Question 194

What JS property is associated with the CSS z-index?

Answer 194

zIndex

Question 195

What properties of an event object give the coordinates of the element that caused that event?

Answer 195

clientX/clientY or screenX/screenY

Question 196

The clientX & clientY properties are relative to what?

Answer 196

The upper left corner of the client (browser) area.

Question 197

The screenX & screenY properties are relative to what?

Answer 197

To the upper left corner of the user’s screen (monitor).

Question 198

What 2 window object methods all us to animate objects in JS?

Answer 198

setTimeout and setInterval

Question 199

What does JS’s “static scoping” entail?

Answer 199

Inner functions have access to the variables/parameters of its outer functions.

Question 200

What does JS’s “closure” entail?

Answer 200

The scope that an inner function enjoys continues even after the parent functions have returned.

Question 201

What is the canvas element in html? (as of HTML5)

Answer 201

It creates a rectangle into which bit-mapped graphics can be drawn using JavaScript.

Question 202

What does the navigator give you access to? (As of HTML5)

Answer 202

Browser information, such as language, userAgent, cookieEnabled, appVersion, appName.

Question 203

What makes a webpage dynamic?

Answer 203

Client side scripting & server side scripting (which generates content before sending it to the client).

Question 204

When is ‘value’ used over ‘innerHTML’?

Answer 204

For form elements.

Question 205

What does .innerHTML return?

Answer 205

The child elements/text of the calling object.

Question 206

What are the 3 phases of the DOM2 event model?

Answer 206

(1) Capture phase
(2) Target phase
(3) Bubbling phase