Chapter 4: Expressions and Operators

Question 1

Object and array _______ are expressions whose value is a newly created object or array

Answer 1

initializers

Question 2

An _____ ______ is a comma-separated list of expressions contained within square
brackets.

Answer 2

array initializer
[] // An empty array: no expressions inside brackets means no elements
[1+2,3+4] // A 2-element array. First element is 3, second is 7

Question 3

Undefined elements can be included in an array literal by simply _______ value between commas.

Answer 3

omitting
var sparseArray = [1,,,,5];

Question 4

Object initializer expressions are like array initializer expressions, but the square brackets are replaced by ____ _____

Answer 4

curly brackets
var p = { x:2.3, y:-1.2 }; // An object with 2 properties
var q = {}; // An empty object with no properties
q.x = 2.3; q.y = -1.2; // Now q has the same properties as p

Question 5

Object literals can be nested

Answer 5

True
var rectangle = { upperLeft: { x: 2, y: 2 },
lowerRight: { x: 4, y: 5 } };

Question 6

A property access expression evaluates to the value of an _____ property or an ______
element

Answer 6

object, array

Question 7

A property access expression evaluates to the value of an object property or an array
element

Answer 7

expression . identifier
expression [ expression ]

Question 8

If the value is not an
object (or array), it is converted to one

Answer 8

True

Question 9

An ______ expression is JavaScript’s syntax for calling (or executing) a function or
method.

Answer 9

invocation
f(0) // f is the function expression; 0 is the argument expression.
Math.max(x,y,z) // Math.max is the function; x, y and z are the arguments.
a.sort() // a.sort is the function; there are no arguments.

Question 10

An ______ _____ expression creates a new object and invokes a function (called a
constructor) to initialize the properties of that object.

Answer 10

object creation

Question 11

Object creation expressions are
like invocation expressions except that they are prefixed with the keyword _____

Answer 11

new
new Object()
new Point(2,3)

Question 12

JavaScript supports one ternary operator, the conditional operator ___, which combines three expressions into a single expression.

Answer 12

?:

Question 13

The ______ operator also has side
effects: deleting a property is like (but not the same as) assigning undefined to the
property.

Answer 13

delete

Question 14

Although _____ is one of the highest-priority operators, the _____ operation is performed on the result of the two property accesses and the function invocation.

Answer 14

typeof

Question 15

The binary ___ operator adds numeric operands or concatenates string operands:

Answer 15

+

Question 16

Examples of + operation for different types

Answer 16

1 + 2 // => 3: addition
“1” + “2” // => “12”: concatenation
“1” + 2 // => “12”: concatenation after number-to-string
1 + {} // => “1[object Object]”: concatenation after object-to-string
true + true // => 2: addition after boolean-to-number

Question 17

Bitwise operators

Answer 17

&, |, ^, ~, &laquo_space;(shift left),&raquo_space; shift right with sign,&raquo_space;> (shift right with zero fill)

Question 18

The ____ operator is
known as the strict equality operator (or sometimes the identity operator), and it checks
whether its two operands are “identical” using a strict definition of sameness

Answer 18

===

Question 19

The ____
operator is known as the equality operator; it checks whether its two operands are
“equal” using a more relaxed definition of sameness that allows type conversions

Answer 19

==

Question 20

The strict equality operator === evaluates its operands, and then compares the two
values as follows, performing no type conversion:

Answer 20

• If the two values have different types, they are not equal.
• If both values are null or both values are undefined, they are equal.
• If both values are the boolean value true or both are the boolean value false, they
  are equal

Question 21

Comparison operator examples

Answer 21

1 + 2 // Addition. Result is 3.
“1” + “2” // Concatenation. Result is “12”.
“1” + 2 // Concatenation. 2 is converted to “2”. Result is “12”.
11 < 3 // Numeric comparison. Result is false.
“11” < “3” // String comparison. Result is true.
“11” < 3 // Numeric comparison. “11” converted to 11. Result is false.
“one” < 3 // Numeric comparison. “one” converted to NaN. Result is false

Question 22

The ___ operator expects a left-side operand that is or can be converted to a _____. It
expects a right-side operand that is an _____.

Answer 22

in, string, object

Question 23

The ______ operator expects a left-side operand that is an object and a right-side
operand that identifies a class of objects

Answer 23

instanceof

Question 24

The behavior of ___ is sometimes called “short circuiting

Answer 24

&&

Question 25

JavaScript uses the ___ operator to assign a value to a variable or property

Answer 25

=

Question 26

a <<= b

Answer 26

a = a << b

Question 27

&= a &= b

Answer 27

a = a & b

Question 28

Like many interpreted languages, JavaScript has the ability to interpret strings of JavaScript source code, evaluating them to produce a value. JavaScript does this with the global function _____

Answer 28

eval() eval("3+2") // => 5

Question 29

x > 0 ? x : -x

Answer 29

// The absolute value of x

Question 30

?:

Answer 30

The operands of the conditional operator may be of any type. The first operand is evaluated and interpreted as a boolean. If the value of the first operand is truthy, then the second operand is evaluated, and its value is returned. Otherwise, if the first operand is falsy, then the third operand is evaluated and its value is returned.

Question 31

For ?: operator, Only one of the second and third operands is evaluated, never both

Answer 31

true

Question 32

______ is a unary operator that attempts to delete the object property or array element specified as its operand

Answer 32

delete

Question 33

The ______ operator is a binary operator whose operands may be of any type. It evaluates its left operand, evaluates its right operand, and then returns the value of the right operand

Answer 33

comma