Datatypes and variables

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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. 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 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