1. JavaScript, Third Edition
Chapter 2
Data Types and Operators

2. JavaScript, Third Edition
Objectives
Work with variables
Study data types
Use expressions and operators
Work with strings
Study operator precedence
JavaScript, Third Edition

3. JavaScript, Third Edition
Variables
Values that a program stores in computer memory
Similar to a storage locker
To use in a program:
Write a statement that creates the variable
Assign it a name
Assigning a value to a variable is the same as storing a value in it
JavaScript, Third Edition

4. JavaScript, Third Edition
Variable names
Name you assign to a variable is called an identifier
Rules and conventions when naming a variable:
Identifiers must begin with an uppercase or lowercase ASCII letter, dollar sign ($), or underscore ( _ )
You can use numbers in an identifier, but not as the first character
You cannot include spaces in an identifier
You cannot use reserved words for identifiers
JavaScript, Third Edition

5. JavaScript, Third Edition
Variable Names (Cont.)
Reserved words (keywords):
Special words part of the JavaScript language
JavaScript, Third Edition

6. JavaScript, Third Edition
Declaring Variables
In JavaScript, the reserved keyword var is used to create variables
Creating a variable is called declaring the variable
Assign a specific value to, or initialize, the variable by using the syntax:
Var variable_name = value;
The value assigned to a variable can be a literal string or a numeric value
JavaScript, Third Edition

7. Declaring Variables (Cont.)
When assigning a literal string value to a variable:
Enclose text in quotation marks
When assigning a numeric value to a variable:
Do not enclose value in quotation marks
You can declare multiple variables in the statement using a single var keyword followed by a series of variable names and assigned values separated by commas
JavaScript, Third Edition

8. JavaScript, Third Edition
Modifying Variables
You can change the variable’s value at any point in a script:
Use a statement that includes variable’s name, followed by an equal sign, followed by the value to assign to the variable
JavaScript, Third Edition

9. JavaScript, Third Edition
Data Types
Specific category of information that a variable contains
Helps determine how much memory the computer allocates for data stored in the variable
Data type also governs the kinds of operations that can be performed on a variable
JavaScript, Third Edition

10. JavaScript, Third Edition
Data Types (Cont.)
Data types that can be assigned only a single value are called primitive types
JavaScript supports six primitive data types
JavaScript, Third Edition

11. JavaScript, Third Edition
Data Types (Cont.)
The null value
data type/value that can be assigned to a variable
Indicates the variable does not contain a usable value
A variable with a value of “null” has a value assigned to it
Null is really “no value”
You assign the “null” value to a variable when you want to ensure that the variable does not contain any data
JavaScript, Third Edition

12. JavaScript, Third Edition
Data Types (Cont.)
The JavaScript language also supports reference, or composite, data types
Reference data types:
Can contain multiple values or complex types of information
As opposed to single values stored in primitive data types
JavaScript, Third Edition

13. JavaScript, Third Edition
Data Types (Cont.)
Three reference data types supported by the JavaScript language are
Functions
Objects
Arrays
JavaScript, Third Edition

14. JavaScript, Third Edition
Data Types (Cont.)
Strongly typed programming languages
Require you to declare the data types of variables
Also known as static typing
Data types do not change after they have been declared
Loosely typed programming languages
Do not require you to declare the data types of variables
Also known as dynamic typing
Data types can change after they have been declared
JavaScript, Third Edition

15. JavaScript, Third Edition
Data Types (Cont.)
JavaScript is a loosely typed programming language
You are not required, and not allowed, to declare the data type of variables
JavaScript interpreter
Automatically determines what type of data is stored in a variable
Assigns the variable’s data type accordingly
JavaScript, Third Edition

16. JavaScript, Third Edition
Numeric Data Types
Are an important part of any programming language
Are particularly useful for arithmetic calculations
JavaScript supports two numeric data types
Integers
Floating-point numbers
JavaScript, Third Edition

17. Numeric Data Types (Cont.)
Integer
Positive or negative number with no decimal places
Can range from (-253) to (253)
Floating-point number
Contains decimal places OR
Written in exponential notation
Exponential notation, or scientific notation
Shortened format for writing very large numbers or numbers with many decimal places
JavaScript, Third Edition

18. JavaScript, Third Edition
Boolean Values
Logical value of true or false
Can also be thought of as being yes or no, or on or off
Most often used for
Deciding which parts of a program should execute
Comparing data
In JavaScript programming, you can only use the words true and false to indicate Boolean values
JavaScript, Third Edition

19. JavaScript, Third Edition
Boolean Values (Cont.)
In other programming languages, you can use the integer values of 1 and 0 to indicate Boolean values of true and false
1 indicates true and 0 indicates false
JavaScript converts the values true and false to the integers 1 and 0 when necessary
JavaScript, Third Edition

20. JavaScript, Third Edition
Arrays
Contain set of data represented by a single variable name
Collection of variables contained within a single variable
Use arrays when you want to store groups or lists of related information in a single, easily managed location
JavaScript, Third Edition

21. JavaScript, Third Edition
Arrays (Cont.)
Represented in JavaScript by the Array object:
Contains a special constructor named Array() which is used for creating an array
Constructor:
special type of function used as the basis for creating reference variables
JavaScript, Third Edition

22. JavaScript, Third Edition
Arrays (Cont.)
Create new arrays by using the keyword new and the Array() constructor with the following syntax:
Var arrayName = new Array(numberƒofƒelements);
Within the parentheses of the Array() construction
Include an integer to represent the number of elements to be contained in the array
Each piece of data contained in an array is called an element
JavaScript, Third Edition

23. JavaScript, Third Edition
Arrays (Cont.)
The numbering of elements within an array starts with an index number of zero (0)
Index number:
An element’s numeric position within the array
Refer to a specific element by enclosing its index number in brackets at the end of the array name
JavaScript, Third Edition

24. JavaScript, Third Edition
Arrays (Cont.)
Assign values to individual array elements in the same fashion as you assign values to a standard variable:
EXCEPT you include the index for an individual element of the array
When you create a new array with the Array() constructor:
Declaring the number of array elements is optional
JavaScript, Third Edition

25. Expressions and Operators
Literal value or variable or a combination of literal values, variables, operators, and other expressions that can be evaluated by the JavaScript interpreter to produce a result
Use operands and operators to create expressions in JavaScript
Operands
Variables and literals contained in an expression
Literal
Value such as a literal string or a number
JavaScript, Third Edition

26. Expressions and Operators (Cont.)
Symbols used in expressions to manipulate operands, such as the addition operator (+) and multiplication operator (*)
Binary operator
Requires an operand before and after the operator
Unary operator
Requires a single operand either before or after the operator
JavaScript, Third Edition

27. Expressions and Operators (Cont.)
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28. JavaScript, Third Edition
Arithmetic Operators
Arithmetic operators
Used in JavaScript to perform mathematical calculations, such as addition
Also used to return the modulus of a calculation:
Remainder left when you divide one number by another number
JavaScript, Third Edition

29. Arithmetic Binary Operators
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30. Arithmetic Unary Operators
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31. Arithmetic Unary Operators (Cont.)
The increment (++) and decrement (--) unary operators can be used as prefix or postfix operators
A prefix operator is placed before a variable
A postfix operator is placed after a variable
JavaScript, Third Edition

32. JavaScript, Third Edition
Assignment Operators
Assignment operators are used for assigning a value to a variable
JavaScript includes other assignment operators called compound assignment operators:
Perform mathematical calculations on variables and literal values in an expression, and then assign a new value to the left operand
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33. Assignment Operators (Cont.)
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34. Assignment Operators (Cont.)
JavaScript, Third Edition

35. Comparison and Conditional Operators
Comparison operators:
Used to compare two operands and determine if one numeric value is greater than another
A Boolean value of true or false is returned after two operands are compared
JavaScript, Third Edition

36. Comparison and Conditional Operators (Cont.)
JavaScript, Third Edition

37. Comparison and Conditional Operators (Cont.)
Comparison operator is often used with the conditional operator:
Executes one of two expressions, based on the results of a conditional expression
The syntax for the conditional operator is conditional expression ? expression1: expression2;
JavaScript, Third Edition

38. JavaScript, Third Edition
Logical Operators
Logical operators are used for comparing two Boolean operands for equality
JavaScript, Third Edition

39. JavaScript, Third Edition
Working With Strings
A text string:
Contains zero or more characters surrounded by double or single quotation marks
Can be used as literal value or can be assigned to a variable
Literal strings can be also be assigned a zero-length string value:
Called an empty string
JavaScript, Third Edition

40. Escape Characters and Sequences
Tells compiler or interpreter that the character following it has a special purpose
In JavaScript, the escape character is the backslash ( \ )
Placing a backslash in front of an apostrophe tells the JavaScript interpreter:
Apostrophe is to be treated as a regular keyboard character
JavaScript, Third Edition

41. Escape Characters and Sequences (Cont.)
the combination of the escape character with other characters is called an escape sequence
JavaScript, Third Edition

42. JavaScript, Third Edition
String Operators
Two operators used with strings:
(+)
(+=)
When used with strings, the plus sign is known as the concatenation operator (+):
Used to combine two strings
JavaScript, Third Edition

43. JavaScript, Third Edition
Special Operators
JavaScript, Third Edition

44. Special Operators (Cont.)
One special operator is the typeof operator
Useful because data type of variables can change during course of program execution
Use to determine the data type of a variable
Syntax is typeof(variablename);
JavaScript, Third Edition

45. Special Operators (Cont.)
JavaScript, Third Edition

46. JavaScript, Third Edition
Operator Precedence
Operator precedence:
Order in which operations in expression are evaluated
When performing operations with operators in the same precedence group
The order of precedence is determined by the operator’s associativity
That is, the order in which operators of equal precedence execute
JavaScript, Third Edition

47. Operator Precedence (Cont.)
JavaScript, Third Edition

48. JavaScript, Third Edition
Chapter Summary
Variables
Values a program stores in computer memory
Data type
Specific category of information that a variable contains
Array
Contains a set of data represented by a single variable name
JavaScript, Third Edition

49. Chapter Summary (cont.)
Constructor
Special type of function used as basis for creating variables of reference data types
Operands
Variables and literals contained in an expression
JavaScript, Third Edition

50. Chapter Summary (cont.)
Operators
Symbols used in expressions to manipulate operands, such as the addition operator (+) and multiplication operator (*)
Operator precedence
Order in which operations in an expression are evaluated
JavaScript, Third Edition