View source for Datatypes and variables

{{JSTuTToC}}

=Data types=
Though JavaScript is a [http://en.wikipedia.org/wiki/Weak_typing 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. The return value of a function which is actually not returning a value, is of type undefined.
* '''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 [http://en.wikipedia.org/wiki/IEEE_754 64-bit format IEEE 754] values including the special values ''Not-a-Number'' (NaN), ''positive infinity'' (Infinity), and ''negative infinity'' (-Infinity). Calculating with numbers is done like in C(++/#), Java, Python, Pascal, PHP, and similar languages.
* '''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. Concatenating strings is done similar to C++/C#, Java, and Pascal with the '+' operator.

==Type conversion==