Javascript_JQUERY_Desiging_Modules_User_interface_working_managing_html_codes.pptx

Chapter 2
Murach's JavaScript and jQuery (3rd Ed.)
© 2017, Mike Murach & Associates, Inc.
Getting started
with JavaScript
C2, Slide 1

Objectives
Applied
1. Given the specifications for a JavaScript application that requires
only the skills that you’ve learned so far, code, test, and debug the
application.
Knowledge
1. Describe two ways to include JavaScript in the head of an HTML
document.
2. Describe how JavaScript can be included in the body of an HTML
document.
3. Describe how case-sensitivity, semicolons, and whitespace relate to
the syntax for a JavaScript statement.
4. List the primary rules for creating a JavaScript identifier.
5. Describe the use of JavaScript comments, including “commenting
out” portions of JavaScript code.
C2, Slide 2

Objectives (continued)
6. Describe the three primitive data types used in JavaScript: numeric,
string, and Boolean.
7. Describe the use of variable declarations and assignment statements
with numeric, string, and Boolean data.
8. Describe the use of the arithmetic operators and the rules for
evaluating an arithmetic expression, including order of precedence
and the use of parentheses.
9. Describe the use of the + operator and the n escape sequence when
working with strings.
10.Describe the syntax for referring to a method or property of an
object.
11.Describe the use of the alert(), prompt(), parseInt(), parseFloat(),
write(), and writeln() methods.
C2, Slide 3

Two attributes of the script element
© 2017, Mike Murach & Associates, Inc. C2, Slide 4
src
type
A script element in the head section
that loads an external JavaScript file
<script src="calculate_mpg.js"></script>

A script element that embeds JavaScript
in the head section
<head>
...
<script>
alert("The Calculate MPG application");
var miles = prompt("Enter miles driven");
miles = parseFloat(miles);
var gallons =
prompt("Enter gallons of gas used");
gallons = parseFloat(gallons);
var mpg = miles/gallons;
mpg = parseInt(mpg);
alert("Miles per gallon = " + mpg);
</script>
</head>

Terms
 external JavaScript file
 embedded JavaScript
C2, Slide 6

JavaScript in the body of an HTML document
<p>
<script>
var today = new Date();
document.write("Current date: ");
document.write(today.toDateString());
</script>
</p>
<p>© 
<script>
document.write( today.getFullYear() );
</script>
, San Joaquin Valley Town Hall
</p>

The result of the JavaScript in a web browser

A noscript element in the body
of an HTML document
<p>© 
<script>
document.write( today.getFullYear() );
</script>
<noscript>2017</noscript>
, San Joaquin Valley Town Hall
</p>

A noscript element at the start
of an HTML document
<h2>
<noscript>
To get the most from this website,
please enable JavaScript.
</noscript>
</h2>

A block of JavaScript code
var joinList = function () {
var emailAddress1 = $("email_address1").value;
if (emailAddress1 == "") {
alert("Email Address is required.");
} else if (emailAddress2 == "") {
alert("Second Email Address is required.");
} else if (emailAddress1 !== emailAddress2) {
alert("Second Email entry must equal first
entry.");
} else if ($("first_name").value == "") {
alert("First Name is required.");
} else {
$("email_form").submit();
}
}

The basic syntax rules for JavaScript
 JavaScript is case-sensitive.
 Each JavaScript statement ends with a semicolon.
 JavaScript ignores extra whitespace within statements.
C2, Slide 12

How to split a statement over two or more lines
 Split a statement after:
an arithmetic or relational operator like +, -, *, /, =, ==, >, or <
an opening brace ( { ), bracket ( [ ), or parenthesis
a closing brace ( } )
 Do not split a statement after:
an identifier, a value, or the return keyword
a closing bracket ( ] ) or parenthesis

Rules for creating identifiers
 Identifiers can only contain letters, numbers, the underscore, and
the dollar sign.
 Identifiers can’t start with a number.
 Identifiers are case-sensitive.
 Identifiers can be any length.
 Identifiers can’t be the same as reserved words.
 Avoid using global properties and methods as identifiers.

Valid identifiers in JavaScript
subtotal
index_1
$
taxRate
calculate_click
$log
C2, Slide 15

Camel casing versus underscore notation
taxRate tax_rate
calculateClick calculate_click
emailAddress email_address
futureValue future_value

Naming recommendations for identifiers
 Use meaningful names. That way, your identifiers aren’t likely to
be reserved words or global properties.
 Be consistent: Either use camel casing (taxRate) or underscores
(tax_rate) to identify the words within the variables in your
scripts.
 If you’re using underscore notation, use lowercase for all letters.

JavaScript code with the comments highlighted
/* this application validates a user's entries for
joining our email list
*/
var $ = function(id) { // the $ function
return document.getElementById(id);
}
// this function gets and validates the user entries
var joinList = function() {
var firstName = $("first_name").value;
var isValid = true;
// validate the first entry
if (emailAddress1 == "") {
$("email_address1_error").firstChild.nodeValue =
"This field is required.";
isValid = false; // set valid switch to off
} else {
$("email_address1_error").firstChild.nodeValue = "";
}
// validate the second entry
...
...
};

The basic syntax rules for comments
 Block comments begin with /* and end with */.
 Single-line comments begin with two forward slashes and
continue to the end of the line.
Guidelines for using comments
 Use comments to describe portions of code that are hard to
understand.
 Use comments to disable portions of code that you don’t want to
test.
 Don’t use comments unnecessarily.

Terms
 statement
 whitespace
 identifier
 camel casing
 comment
 comment out
C2, Slide 20

JavaScript’s primitive data types
 Number
 String
 Boolean

Examples of number values
15 // an integer
-21 // a negative integer
21.5 // a decimal value
-124.82 // a negative decimal value
-3.7e-9 // floating-point notation for -0.0000000037
The number data type
 A number value can be an integer or a decimal value.
 In JavaScript, decimal values are stored as floating-point numbers.
 If a result is stored in a number data type that is larger or smaller
than the data type can store, it will be stored as the value Infinity
or -Infinity.

Examples of string values
"JavaScript" // a string with double quotes
'String Data' // a string with single quotes
"" // an empty string
The string data type
 A string value is surrounded by double quotes or single quotes.
The string must start and end with the same type of quotation
mark.
 An empty string is a string that contains no characters. It is
entered by typing two quotation marks with nothing between
them.

The two Boolean values
true // equivalent to true, yes, or on
false // equivalent to false, no, or off
The Boolean data type
 A Boolean value can be true or false. Boolean values are often
used in conditional statements.

How to declare and assign a value to a variable
in two statements
Syntax
var variableName;
variableName = value;
Examples
var counter; // declaration statement;
// value is undefined
counter = 1; // assignment statement;
// value is 1
var sum, average; // declares two variables
sum = 0, average = 0; // assigns values to two
// variables

How to declare and assign a value to a variable
in one statement
Syntax
var variableName = value;
Examples
var count = 1; // integer value of 1
var subtotal = 74.95; // decimal value of 74.95
var name = "Joseph"; // string value of "Joseph"
var email = ""; // empty string
var isValid = false; // Boolean value of false
var total = subtotal; // assigns value of
subtotal variable
var x = 0, y = 0; // declares and assigns
values to 2 variables

Terms
 variable
 declare a variable
 assignment statement
 assignment operator
 literal value
 literal
 string literal
 numeric literal

JavaScript’s arithmetic operators
Operator Name Description
+ Addition Adds two operands.
- Subtraction Subtracts the right operand from the
left operand.
* Multiplication Multiplies two operands.
/ Division Divides the right operand into the left
operand. The result is always a
floating-point number.
% Modulus Divides the right operand into the left
operand and returns the remainder.
++ Increment Adds 1 to the operand.
-- Decrement Subtracts 1 from the operand.

The order of precedence
for arithmetic expressions
Order Operators Direction Description
1 ++ Left to right Increment operator
2 -- Left to right Decrement operator
3 * / % Left to right Multiplication, division,
modulus
4 + - Left to right Addition, subtraction

Examples of simple arithmetic expressions
Example Result
5 + 7 12
5 - 12 -7
6 * 7 42
13 / 4 3.25
13 % 4 1
counter++ counter = counter + 1
counter-- counter = counter – 1
3 + 4 * 5 23 (the multiplication is done first)
(3 + 4) * 5 35 (the addition is done first)
13 % 4 + 9 10 (the modulus is done first)
13 % (4 + 9) 0 (the addition is done first)

Code that calculates sales tax
var subtotal = 200;
var taxPercent = .05;
var taxAmount = subtotal * taxPercent; // 10
var total = subtotal + taxAmount; // 210
Code that calculates the perimeter of a rectangle
var width = 4.25;
var length = 8.5;
var perimeter = (2 * width) + (2 * length)
// (8.5 + 17) = 25.5

The most useful compound assignment operators
Operator Description
+= Adds the result of the expression to the variable.
-= Subtracts the result of the expression from the
variable.
*= Multiplies the variable value by the result of the
expression.
Statements with compound assignment operators
var subtotal = 74.95;
subtotal += 20.00; // subtotal = 94.95
var counter = 10;
counter -= 1; // counter = 9
var price = 100;
price *= .8; // price = 80

Three ways to increment a counter variable by 1
var counter = 1; // counter = 1
counter = counter + 1; // counter now = 2
counter += 1; // counter now = 3
counter++; // counter now = 4

A floating-point result that isn’t precise
var subtotal = 74.95; // subtotal = 74.95
var salesTax = subtotal * .1; // salesTax =
7.495000000000001
A problem with some arithmetic operations
 When you do some types of arithmetic operations with decimal
values, the results aren’t always precise. That’s because decimal
values are stored internally as floating-point numbers.
 The primary problem with this is that an equality comparison may
not return true.

Terms related to arithmetic expressions
 arithmetic expression
 arithmetic operators
 order of precedence
 compound assignment operators

The concatenation operators for strings
+ Concatenates two values.
+= Adds the result of the expression
to the end of the variable.
How to concatenate string variables
with the + operator
var firstName = "Grace", lastName = "Hopper";
var fullName = lastName + ", " + firstName;
// fullName is "Hopper, Grace"
How to concatenate string variables
with the += operator
var firstName = "Grace", lastName = "Hopper";
var fullName = lastName; // fullName is "Hopper"
fullName += ", "; // fullName is "Hopper, "
fullName += firstName; // fullName is "Hopper, Grace"

How to concatenate a string and a number
with the + operator
var months = 120;
var message = "Months: ";
message = message + months; // message is "Months: 120"
How to concatenate a string and a number
with the += operator
var months = 120;
var message = "Months: ";
message += months; // message is "Months: 120"

Some of the escape sequences that can be used
in strings
n Starts a new line in a string.
" Puts a double quotation mark in a string.
' Puts a single quotation mark in a string.
How escape sequences can be used in a string
var message = "A valid variable namencannot start with a number.";
var message = "This isn't the right way to do this.";

Terms related to strings
 concatenate (join) strings
 concatenation operators
 string expression
 escape sequences

Common methods of the window object
alert(string)
prompt(string, default)
print()
The syntax for calling a method of an object
objectName.methodName(parameters)
A statement that calls the alert() method
of the window object
window.alert("This is a test of the alert method");

A statement that calls the prompt() method
with the object name omitted
var userEntry =
prompt("This is a test of the prompt method", 100);
The prompt dialog box that’s displayed

One property of the window object
location
The syntax for accessing a property of an object
objectName.propertyName
A statement that displays
the URL of the current page
alert(window.location);

Two methods of the window object
parseInt(string)
parseFloat(string)
The parsing that’s done by the parse methods
 Only the first number in the string is returned.
 Leading and trailing spaces are removed.
 If the first character cannot be converted to a number, NaN is
returned.

Examples that use the parseInt()
and parseFloat() methods
var entryA = prompt("Enter any value", 12345.6789);
alert(entryA); // displays 12345.6789
entryA = parseInt(entryA);
alert(entryA); // displays 12345
var entryB = prompt("Enter any value", 12345.6789);
alert(entryB); // displays 12345.6789
entryB = parseFloat(entryB);
var entryC = prompt("Enter any value", "Hello");
alert(entryC); // displays Hello
entryC = parseInt(entryC);
alert(entryC); // displays NaN

The same examples with the parse methods
embedded in the alert() method
var entryA = prompt("Enter any value", 12345.6789);
alert(entryA); // displays 12345.6789
alert(parseInt(entryA)); // displays 12345
var entryB = prompt("Enter any value", 12345.6789);
alert(parseFloat(entryB)); // displays 12345.6789
var entryC = prompt("Enter any value", "Hello");
alert(entryC); // displays Hello
alert(parseInt(entryC)); // displays NaN

Two methods of the document object
write(string)
writeln(string)

Examples of the write() and writeln() methods
<body>
<script>
document.write("<h1>Welcome to our site!</h1>");
document.write("Today is ");
document.write(today.toDateString());
document.write("<br>");
document.writeln("Today is ");
document.writeln(today.toDateString());
document.write("<br>");
</script>
<script>
document.writeln("Welcome to our site!");
document.writeln("Today is Monday.");
</script>
<script>
document.writeln("<pre>Welcome to our site!");
document.writeln("Today is Monday.</pre>");
</script>
</body>

The output in a browser

Terms related to objects
 object
 method
 property
 call a method
 parameter
 window object
 global object
 dot operator
 document object

The Calculate MPG application
The first prompt dialog box
The second prompt dialog box

The Calculate MPG application (continued)
The alert dialog box that displays the result

The HTML and JavaScript for the application
<html>
<head>
<title>The Calculate MPG Application</title>
<script>
var miles = prompt("Enter miles driven");
miles = parseFloat(miles);
var gallons = prompt("Enter gallons of gas used");
gallons = parseFloat(gallons);
var mpg = miles/gallons;
mpg = parseInt(mpg);
alert("Miles per gallon = " + mpg);
</script>
</head>
<body>

<h1>Thanks for using the Miles Per Gallon
application!</h1>
</body>
</html>

The results of the Test Scores application
in a browser

The HTML and JavaScript for the application
<html>
<head>
<title>Average Test Scores</title>
<script>
var entry;
var average;
var total = 0;
//get 3 scores from user and add them together
entry = prompt("Enter test score");
entry = parseInt(entry);
var score1 = entry;
total = total + score1;
var score2 = entry;

The HTML and JavaScript (cont.)
var score3 = entry;
//calculate the average
average = parseInt(total/3);
</script>
</head>
<body>
<script>
document.write("<h1>The Test Scores App</h1>");
document.write("Score 1 = " + score1 + "<br>" +
"Score 2 = " + score2 + "<br>" +
"Score 3 = " + score3 + "<br><br>" +
"Average score = " + average + "<br><br>");
</script>
Thanks for using the Test Scores application!
</body>
</html>

Exercise 2-1 Modify the MPG application
Display the output in the browser, not in an alert dialog
box.

Exercise 2-3 Create a simple application
Start with the MPG app and change it into a new app.

Extra 2-1 Convert Fahrenheit to Celsius
The prompt dialog box
The alert dialog box
To convert F to C subtract 32 from F and multiply by 5/9.

Short 2-1 Modify the Test Scores application
Estimated time: 10 to 20 minutes.
Provide for a fourth score and display the results in a
dialog box.

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