Defining Variables in Javascript.

Javascript variables

How to define Javascript variables?

• JavaScript is a loosely typed language, meaning that no variable can clearly be defined with a specific datatype.
• We are using the general type, var, for all datatype (numbers, booleans, strings, objects and so on).

  var myInteger=10;
  var myString="10";
  var myboolean=true;
  // It is legal to omit the "var" keyword, but not recommended:
  myvariable=10;

• The semicolon serves to separate statements from each other.

  var counter = 3; var weight = 40;
  // or the same without var keyword:
  counter = 3; weight = 40;

• However you can omit the semicolon for each of your statements placed on a separate lines.

  counter = 3
  weight = 40

• BUT - It is not a god practice to omit the semicolon.

  // For instance: 
  return
  true;
  // is NOT the same as:
  return true;

• You can also declare several variables and different types of variables with the same var keyword:

  <script type="text/javascript">
    var a=4;
    var b="45", c=0, d=true;
    document.write("a: "+ a +" b: "+b);
    document.write(" c: "+ c +" d: "+d);
  </script>

  The result should be:

  a: 4 b: 45 c: 0 d: true

Variable name and other identifiers in javascript.

• An identifier is used to name variables and functions, and to provide labels for certain loops.
  1. An identifier must start with a letter, an underscore (_), or a dollar sign ($).
  2. Subsequent characters for the identifier can be a letter, a digit, an underscore (_), or a dollar sign ($).

  // These names are all legal identifiers:
  i
  variable_name
  version13
  _dummyName
  $myString

• You cannot use reserved keywords as identifiers:

  keyword	keyword	keyword	keyword	keyword
  break	do	if	switch	typeof
  case	else	in	this	var
  catch	false	instanceof	throw	void
  continue	finally	new	true	while
  default	for	null	try	with
  delete	function	return

• You should also avoid these words as identifiers:
  

  keyword	keyword	keyword	keyword	keyword
  arguments	encodeURI	Infinity	Object	String
  Array	Error	isFinite	parseFloat	SyntaxError
  Boolean	escape	isNaN	parseInt	TypeError
  Date	eval	Math	RangeError	undefined
  decodeURI	EvalError	NaN	ReferenceError	unescape
  decodeURIComponent	Function	Number	RegExp	URIError