JavaScript Calculator

noreply@blogger.com (Ron Tinnel) — Sat, 22 Oct 2011 23:56:00 +0000

REVISED: Monday, March 3, 2013

Shown below is a JavaScript Calculator:

--> This JavaScript calculator has the usual precedence rules; however, use parentheses.

Elcric Otto Circle

-->

How to Link to My Home Page

It will appear on your website as:
"Link to ELCRIC OTTO CIRCLE's Home Page"

JavaScript Introduction

noreply@blogger.com (Ron Tinnel) — Sat, 22 Oct 2011 16:16:00 +0000

REVISED: Sunday, March 3, 2013

I. JAVASCRIPT

A. Programming Tool

1. Statements

JavaScript is a scripting language that gives HTML designers a programming tool.

A JavaScript statement is a command to a browser.

It is normal to add a semicolon at the end of each executable statement.

Each statement is executed by the browser in the sequence they are written.

JavaScript statements can be grouped together in blocks. Blocks start with a left curly bracket {, and end with a right curly bracket }. A block is used to group statements together in a function or in a condition, where a group of statements should be executed if a condition is met.

JavaScript is case sensitive.

JavaScripts can be put in the <body> and in the <head> sections of an HTML page.

2. Comments

Single line JavaScript comments start with //. Multi line comments start with /* and end with */.

3. Rules for Variables

You declare JavaScript variables with the var keyword.

Variable names are case sensitive; z and Z are two different variables.

Variable names must begin with a letter or the underscore character.

When you assign a text value to a variable, use quotes around the value.

A variable declared within a JavaScript function becomes LOCAL and can only be accessed within that function. Local variables are destroyed when you exit the function. Variables declared outside a function become GLOBAL. Global variables are destroyed when you close the page. If you declare a variable, without using "var", the variable always becomes GLOBAL. If you assign values to variables that have not yet been declared, the variables will automatically be declared as global variables.

4. Assignment Operators

Given x=20 and y=10 then:

Assignment = x=y x=y x=10 y=10
Addition += x+=y x=x+y x=30 y=10
Subtraction -= x-=y x=x-y x=10 y=10
Multiplication *= x*=y x=x*y x=200 y=10
Division /= x/=y x=x/y x=2 y=10
Modulus %= x%=y x=x%y x=0 y=10
Increment ++ x=++y x=11 y=11
x=y++ x=10 y=11
Decrement -- x=--y x=9 y=9
x=y-- x=10 y=9

B. Uses

JavaScript can be used to:

1. React

React to events such as when a page has finished loading or when a user clicks on an HTML element.

2. Read and Write

Read and write HTML elements.

3. Validate

Validate form data before it is submitted to a server. This saves the server from extra processing.

4. Detect

Detect the visitor's browser.

5. Create

Create cookies and store and retrieve information on the visitor's computer.

C. Browser Support

Some Browsers do Not Support JavaScript.

Browsers that do not support JavaScript, will display JavaScript as page content.

To prevent them from doing this, and as a part of the JavaScript standard, the HTML comment tag should be used to "hide" the JavaScript.

Just add an HTML comment tag  (end of comment) after the last JavaScript statement, as shown in the first example below:

II. JAVASCRIPT EXAMPLES

A. Date Button

The following is an example of using JavaScript to create a button that displays the date:

<html>
<head>
<script type="text/javascript">



</script>
</head>
<body>

<h1>Please left click button for today's date:</h1>
<p id="demo">JavaScript Date Button.</p>

<button type="button" onclick="displayDate()">Display Date</button>

</body>
</html>

EXAMPLE OUTPUT:

Sat Oct 22 2011 19:20:11 GMT-0400 (Eastern Daylight Time)

Elcric Otto Circle

-->

How to Link to My Home Page

It will appear on your website as:
"Link to ELCRIC OTTO CIRCLE's Home Page"