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

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