The Web Warrior Guide to Web Design Technologies

1
The Web Warrior Guide to Web Design Technologies
Chapter 14 JavaScript Part II
2
Objectives

• In this chapter you will
• Study data types
• Use expressions and arithmetic, assignment,
  comparison, conditional, and logical operators
• Work with strings

3
Data Types

• A data type is a specific category of information
  that a variable contains.
• A variables specific data type is very important
  because the data type helps determine how much
  memory the computer will allocate for the data
  stored in the variable.
• The data type also governs the kinds of
  operations that can be performed on a variable.

4
Data Types

• Data types that can only be assigned a single
  value are called primitive types.
• Primitive types Integer, Floating-point number,
  Boolean, String, Undefined, and Null.
• JavaScript supports three reference data types
  Functions, Objects, and Arrays.
• Assigning a null value to a variable indicates
  that the variable does not contain a value.

5
Data Types
6
Data Types

• Strongly-typed programming languages require
  programmers to declare the data type of
  variables.
• Loosely-typed programming languages do not
  require the programmer to declare the data type
  of variables.
• JavaScript is a loosely-typed programming
  language.

7
Data Types

• The data type of a variable can be determined
  using the typeof() operator.
• JavaScript supports two numeric data types
  Integers and Floating-point numbers.
• An Integer is a positive or negative number with
  no decimal place.
• Integer values can range from
• 9007199254740990 to 9007199254740990

8
Data Types

• A Floating-point numbers contain decimal places.
• Exponential notation, or scientific notation, is
  a shortened format for writing very large
  numbers, or numbers with many decimal places.
• The value of 10 is written with an uppercase or
  lowercase E.

9
Data Types

• 2.0e11 means two times 10 to the eleventh
  power.
• Floating-point values that exceed the largest
  positive value of - 1.7976931348623157 x 10 308
  result in a special value of Infinity.
  Floating-point values that exceed the smallest
  negative value of - 5 x 10 -324 result in a
  value of Infinity.

10
Data Types

• A Boolean value is a logical value of true or
  false.
• An Array contains a set of data represented as a
  single variable name.
• Arrays are represented in JavaScript by the Array
  object.
• Array() is a constructor function.
• Each piece of data in the Array is called an
  element.

11
Data Types

• The numbering of elements in the array starts at
  zero.
• A specific array element is referred to by
  enclosing its index number in brackets at the end
  of the array name.
• In JavaScript, the values assigned to an array
  element can be different data types.

12
Data Types

• When an array is created with the Array()
  constructor function, declaring the number of
  array elements is optional.
• The size of an array can change dynamically.
• The number of elements in the array can be
  determined using the length property.
• Values can be assigned to array elements when the
  array is first created.

13
Expressions and Operators

• An expression is a combination of literal values,
  variables, operators, and other expressions that
  can be evaluated by the JavaScript interpreter to
  produce a result.
• Operands are variables and literals contained in
  an expression.
• Operators are symbols used in expressions to
  manipulate operands.

14
Expressions and Operators

• A binary operator requires an operand before and
  after the operator.
• A unary operator requires a single operand either
  before or after the operator.
• Arithmetic operators are used to perform
  mathematical calculations.
• The prefix operator is placed before a variable.

15
Expressions and Operators
16
Expressions and Operators
17
Expressions and Operators
18
Expressions and Operators

• The postfix operator is placed after a variable.
• The increment () and decrement (--) unary
  operators can be used as prefix and postfix
  operators.
• Assignment operators are used for assigning a
  value to a variable.
• Examples of assignment operators , , -, ,
  /, and .

19
Expressions and Operators
20
Expressions and Operators

• Comparison operators are used to compare two
  operands and determine if one numeric value is
  greater than another.
• Examples of comparison operators , , !,
  !, gt, lt, gt, lt.
• The conditional operator executes one of two
  expressions, based on the result of a conditional
  expression. A conditional expression returns a
  Boolean value and determines whether to execute a
  conditional or looping statement.

21
Expressions and Operators

• The syntax of a conditional operator is
• conditional expression ? expression1 expression2
• Logical operators are used for comparing two
  Boolean operands for equality.
• Examples of logical operators , , and !

22
Expressions and Operators

• Operator precedence is the order of priority in
  which operations in an expression are evaluated.
  Expressions are evaluated from left to right,
  with the highest priority precedence evaluated
  first.
• If all the operators in the expression have the
  same priority of precedence, then the expression
  is evaluated from left to right.

23
Expressions and Operators

• Order of precedence from highest to lowest
• Parentheses/brackets/dot ( () .)
• Negation/increment (! - -- typeof void)
• Multiplication/division/modulus ( / )
• Addition/subtraction ( -)
• Comparison (lt lt gt gt)
• Equality ( !)
• Logical and ()
• Logical or ()

24
Expressions and Operators

• Assignment operators ( - / )
• Comma (,)

25
Strings

• The escape character is a special character that
  tells the interpreter that the character
  following it has a special purpose.
• The escape character in JavaScript is \.
• The combination of the escape character with
  other characters is called an escape sequence.
• Examples of escape sequences \n, \b, \f, \\, \

26
Strings
27
Strings

• The concatenation operator for strings is .
• The assignment operator can be used to combine
  two strings.
• The JavaScript String object contains methods for
  manipulating text strings.
• Commonly used methods are big(), blink(),
  bold(), charAt(index), fixed(), fontColor(color),
  fontSize(size), indexOf(text, index), italics()

28
Strings

• The length property determines the number of
  characters in the string.
• Parsing refers to the act of extracting
  characters of substrings from a larger string.

29
Summary

• A data type is the specific category of
  information that a variable contains.
• Data types that can be assigned only a single
  value are called primitive types.
• Reference, or composite, data types can contain
  multiple values or complex types of information.
• Programming languages that require you to declare
  the data types of variables are called
  strongly-typed programming languages.
• Programming languages that do not require you to
  declare the data types of variables are called
  loosely-typed programming languages.

30
Summary

• An Integer is a positive or negative number with
  no decimal places.
• A Floating-point number is a number that contains
  decimal places or is written using exponential
  notation.
• A Boolean value is a logical value of true or
  false.
• An Array is a variable that contains a set of
  data represented by a single variable name.
• An expression is a combination of literal values,
  variables, operators, and other expressions that
  can be evaluated by the JavaScript interpreter to
  produce a result.

31
Summary

• Operands are variables and literals contained in
  an expression.
• Operators are symbols used in expressions to
  manipulate operands.
• Arithmetic operators are operators that are used
  to perform mathematical calculations, such as
  addition, subtraction, multiplication, and
  division, in JavaScript.
• Assignment operators are operators that are used
  for assigning a value to a variable.
• Comparison operators are operators that are used
  to compare two operands to determine if one
  numeric value is greater than another.

32
Summary

• The conditional operator executes one of two
  expressions based on the results of a conditional
  expression.
• Logical operators are used for comparing two
  Boolean operands for equality.
• Operator precedence is the order of priority in
  which operations in an expression are evaluated.
• An escape character is a special character that
  tells the compiler or interpreter that the
  character following it has a special purpose.
• Parsing refers to the act of extracting
  characters or substrings from a larger string.
• The JavaScript String object contains methods for
  manipulating text strings.