Datatypes and variables

Introduction to JavaScript

Integrate JavaScript on webpages Internal JavaScript External JavaScript Inline JavaScript Datatypes and variables Datatypes overview Variables declaration Arrays Implementation Declaration array as object -> properties and methods Anonymous arrays associative arrays/hashtables Functions Declaration Parameters Default values for parameters and variable length parameter lists return values callback functions anonymous functions Objects Class definition, object initialisation, singletons Prototyping concept and inheritance Anonymous objects Objects as associative arrays

Data types

Though JavaScript is a weakly typed programming language, there are some primitive data types between which JavaScript sometimes variables automatically converts:

• null: Null means variable has no value at all. Do not confuse null with 0 (zero)! 0 is just a number, null means just no value or a empty or non-existent reference.
• undefined: A value that is undefined is a value held by a variable right after it has been created and before a value has been assigned to it.
• boolean: A variable of type boolean may hold the special values true or false. If a number value is used where a boolean expression is expected, a zero value will be treated like false and any other value will be treated as true.
• number: This type is a set of values representing integer and floating point numbers. In ECMAScript, the set of values represents the double-precision 64-bit format IEEE 754 values including the special values Not-a-Number (NaN), positive infinity (Infinity), and negative infinity (-Infinity).
• string: A variable of type string is - formally spoken - a finite ordered sequence of at least zero 16-bit unsigned integer values. Practically it is just a string, like you may know from C++ or Java. In C it's like a character array, but with 16 bit characters instead of 8 bit C-char. Single characters of a string can be accessed just like in any other major C-like programming language using square brackets. The first character has index 0.