Expressions and Operators

Question 1

List the operators used in JavaScript

Answer 1

1. Assignment operators
2. Comparison operators
3. Arithmetic operators
4. Bitwise operators
5. Logical operators
6. String operators
7. Conditional (ternary) operator
8. Comma operator
9. Unary operators
10. Relational operators

Question 2

What is an assignment operator?

Answer 2

An assignment operator assigns a value to its left operand based on the value of its right operand

Question 3

What are compound assignment operators?

Answer 3

Compound assignment operators are shorthand for assigning multiple operations

Some examples of compound assignment operators are:

+= - this will add the value of the right operand to the value of the left operand and assign it to the left operand

• = - in the same way as mentioned above this compound assignment subtracts and assigns
• = - this compound assignment multiplies and assigns

/= - this compound assignment divides and assigns

Question 4

What is a comparison operator?

Answer 4

A comparison operator compares its operands and returns a logical value based on whether the comparison is true

The operands can be numerical, string, logical, or object values

Strings are compared based on standard lexicographical ordering, using Unicode values

Question 5

Explain type conversion in JavaScript

Answer 5

In most cases, if the two operands are not of the same type, JavaScript attempts to convert them to an appropriate type for the comparison

This behavior generally results in comparing the operands numerically

Question 6

How do you avoid errors in JavaScript type conversion?

Answer 6

By using the strict equality operators (=== and !==) to perform strict equality and inequality comparisons

These operators do not attempt to convert the operands to compatible types before checking equality

Question 7

List the JavaScript comparison operators

Answer 7

1. Equal ( == )
2. Not equal ( != )
3. Strict equal ( === )
4. Strict not equal ( !== )
5. Greater than ( > )
6. Greater than or equal ( >= )
7. Less than ( < )
8. Less than or equal ( <= )

Question 8

What is an arithmetic operator?

Answer 8

An arithmetic operator takes numerical values (either literals or variables) as their operands and returns a single numerical value

Question 9

List the JavaScript standard arithmetic operators

Answer 9

1. Addition ( + )
2. Subtraction ( - )
3. Multiplication ( * )
4. Division ( / )

Question 10

List the JavaScript non-standard arithmetic operators

Answer 10

1. Remainder ( % )
2. Increment ( ++ )
3. Decrement ( – )
4. Unary negation ( - )
5. Unary plus ( + )
6. Exponentiation operator ( ** )

Question 11

What is a bitwise operator?

Answer 11

A bitwise operator treats their operands as a set of 32 bits (zeros and ones), rather than as decimal, hexadecimal, or octal numbers

For example, the decimal number nine has a binary representation of 1001

Bitwise operators perform their operations on such binary representations, but they return standard JavaScript numerical values

Question 12

List the JavaScript bitwise operators

Answer 12

1. Bitwise AND
2. Bitwise OR
3. Bitwise XOR
4. Bitwise NOT
5. Left shift
6. Sign-propagating right shift
7. Zero-fill right shift

Question 13

What is a logical operator?

Answer 13

Logical operators are typically used with Boolean (logical) values; when they are, they return a Boolean value

However, the && and || operators actually return the value of one of the specified operands, so if these operators are used with non-Boolean values, they may return a non-Boolean value

Question 14

List the JavaScript logical operators

Answer 14

1. Logical AND ( && )
2. Logical OR ( || )
3. Logical NOT ( ! )

Question 15

In which cases does the logical AND operator return true

Answer 15

Only when both operands being evaluated result in true

Question 16

In which cases does the logical AND operator return false

Answer 16

If both operands result in false

Or if either operand results in false

Question 17

In which cases does the logical OR operator return true

Answer 17

If both operands result in true

Or if one of the operands result in true

Question 18

In which cases does the logical OR operator return false

Answer 18

Only when both operands being evaluated result in false

Question 19

Describe the use of the logical NOT operator

Answer 19

This operator takes a single Boolean value and inverts it

If a result evaluated to false before adding NOT ( ! ) it would return true

If the result evaluated to true before adding NOT ( ! ) it would return false

Question 20

Describe “short-circuit” evaluation

Answer 20

As logical expressions are evaluated left to right, they are tested for possible “short-circuit” evaluation using the following rules:

• false && anything is short-circuit evaluated to false
• true || anything is short-circuit evaluated to true

The “anything” part of the above expressions is not evaluated

Question 21

Describe concatenation of String operators in JavaScript

Answer 21

Concatenation is when the plus sign ( + ) is used to join two string values together

This returns a string which is the union of the two operand strings

Question 22

Describe the conditional (ternary) operator in JavaScript

Answer 22

The conditional operator is the only JavaScript operator that takes three operands

The operator can have one of two values based on a condition (Syntax: condition ? val1 : val2)

If “condition” is true, the operator has the value of “val1” otherwise it has the value of “val2”

Question 23

Describe the comma operator

Answer 23

The comma operator ( , ) evaluates both of its operands and returns the value of the last operand

This operator is primarily used inside a for loop, to allow multiple variables to be updated each time through the loop

Question 24

Describe unary operators

Answer 24

A unary operation is an operation with only one operand

Question 25

List unary operators

Answer 25

delete - this operator deletes an object’s property

typeof - this operator returns a string indicating the type of the unevaluated operand (ie string, number, etc)

void - this operator specifies an expression to be evaluated without returning a value

Question 26

Describe relational operators

Answer 26

A relational operator compares its operands and returns a Boolean value based on whether the comparison is true

Question 27

List relational operators

Answer 27

in - this operator returns true if the specified property is in the specified object

instanceof - this operator returns true if the specified object is of the specified object type

Question 28

Describe truthy and falsy values in JavaScript

Answer 28

Due to type coercion (or conversion), every value in JavaScript can be treated as if it were true or false

Question 29

List JavaScript falsy values

Answer 29

1. The traditional Boolean false
2. The number zero
3. An empty string
4. NaN or not a number
5. A variable that has not be assigned a value

Question 30

List JavaScript truthy values

Answer 30

1. The traditional Boolean true
2. Numbers other than zero
3. Strings with content
4. Number calculations
5. True written as a string
6. Zero written as a string
7. False written as a string

Question 31

What is an expression in JavaScript

Answer 31

An expression is any valid unit of code that resolves to a value

There are two types of expressions: those that assign value to a variable, and those that in some sense evaluate and therefore resolve to a value

Question 32

List the JavaScript expression categories

Answer 32

1. Arithmetic - evaluates to a number
2. String - evaluates to a character string
3. Logical - evaluates to true or false
4. Primary expressions - basic keywords and general expressions in JavaScript
5. Left-hand-side expressions - left values are the destination of an assignment

Question 33

Describe primary expressions in JavaScript

Answer 33

this - a JavaScript keyword used to refer to the current object

( ) - the grouping operator used to control the precedence of evaluation in expressions

Question 34

Describe left-hand-side expressions in JavaScript

Answer 34

new - use the new operator to create an instance of a user-defined object type or of one of the built-in object types

super - use the super keyword to call functions on an object’s parent