05/05/2017

13TH DAY AT UKI

JAVASCRIPT

   1.  There are a number of different places where Javascript can be used but the most common place to use it is in a web page. 

                                                                                                               

 

    The HTML defines what the content is.

    CSS defines the appearance of a web page.

    Javascript adds behavior to the web page.

JAVASCRIPT VALUES

       The javascript syntax defines two types of values:

                     1.fixed values

                               fixed values are called literals.

                     2.variable values

                                 variable values are called variables.

JAVASCRIPT VARIABLES

       Javascript variables are containers for storing data values.

       All javascript variables must be identified with unique names.These unique names are called identifiers.

       Names for variables are :

             1.contain letters,digits,underscores and dollar signs.

             2.Names must begin with a letter.

             3.Names can also begin with $.

             4. Names are case sensitive.

             5.reserved words are cannot be used as names.

      In javascript, the equal sign(=) is an "assignment" operator, not an "equal" operator.

      The "equal" operator is written like == in javascript.

EXAMPLE:

        var price1=5;

        var price2=6;

        var total=price1+price2;  

JAVASCRIPT DATA TYPES

     Javascript variables can hold many data types:numbers,strings,objects.

        Examples:

          1.Number

               var length=16;

          2.String

               var lastname="johnson";

          3.Objects

               var X={firstname:"john",lastname:"doe"};

     In programming,data types are important concept.

     To be able to operate on variables,it is important to know something about the type.

     Javascript evaluates expressions from left to right.

     Different sequences can produce different results:

          var X=16+4+"volvo";

               results:20volvo

           

          var X="volvo"+16+4

               results:volvo164

                     Since the first operand is a string, all operands are treated as strings.

          Javascript has dynamic types.

                  This means that the same variables can be used to hold different data types:

             var X;

                 Now X is undefined.

                

             var X=5;

                 Now X is a number.

             var X="john";

                 Now X is a string.