Canvas element - circles and ellipses

Several new elements have been introduced with the release of hTML5. Perhaps the most significant, is the canvas element which now makes it possible to draw, add text and create animations using Javascript. It is also possible to manipulate images.

Javascript Objects

When considering Javascript objects, its worth remembering that javascript is not confined to HTML, It can be used to manipulate XML, which in turn can be used to mirror the table structures found in a database. In fact many websites and Content Management Systems use databases to store information to be displayed on the site and HTML has become a popular front end for such databases.

Javascript objects, in common with other object orientated programming languages, have both properties and methods.

Math Object

The Math object provides functions for basic mathematical operations.

Hexadecimal colour values

This example demonstrates how Javascript can convert between hexadecimal and decimal numbers by prefixing a (hexadecimal) number with 0x. When a hexadecimal number is parsed, it outputs is decimal equivalent.

This little trick avoids having to write a function to do the conversion.

The decimal system

The numbering scheme in everyday use is the decimal (or denary) system and numbers are represented by 10 digits i.e. the numbers 0 to 9.

Counting starts at zero, (see counting wheels below). Rotating the wheel anticlockwise adds 1 to the current count until the number reaches 9 whereupon the count is reset to 0.

Radians and degrees (or angular measure)

When measuring angles we usually measure them in degrees. There are 360 degrees in a circle. I.e. a degree simply divides a circle into 360 segments.
An alternative radial measure is known as a radian. A radian is the angle formed by measuring the radius around the circumference of a circle as show by the diagram. 1 radian is approximately 57.32 degrees.

Operators

The most common operators are mathematical operators; +, -, /, * (add, subtract, divide, multiply) for example. Operators can be split into two groups, comparison operators and assignment or 'action' operators. Comparison operators test to see if two variables relate to each other in the specified way, for example, one variable is a higher number than the other. Other operators perform an action on a variable, such as increasing it by one.

Math constants

JavaScript understands numbers in several formats, allowing you to specify numbers in hex, decimal, and octal. If a 0 precedes a number and there is no number higher than 7, the number is considered to be in octal (base 8) and if the number is preceded by 0x, then it is considered to be in hex (base 16) and can also contain characters A, B, C, D, E, F. Neither may contain decimal points.

With decimal numbers, 12e+4 may be used to replace 12x10⁴ and 12e-4 may be used to replace 12x10^-4 etc.

String Object

The String object is used to manipulate a stored piece of text. String objects are created with new String().

Strings

A string literal is 0 or more characters enclosed in either double, or single quotes. For example

    "Hello World"
    'Sun wind and rain'
    "123"

Strings are a fundamental to any programming language and as well as all the comparison operators strings may be concatenated (joined) together using the concatenation operator, the plus symbol ( + ). for example