JavaScript variables and identifiers

JavaScript Variables

  • JavaScript uses variables which can be thought of as Named Containers.
  • Variables are declared with the 'var' keyword.

    • Example:
    var a;
    var b;

  • Variable names are case sensitive.
  • You can declare multiple variables with the same 'var' keyword.

    • Example: var a, b;

Variable initialization

Example : Variable initialization

var a = 10;
var b = 20;

Variable Scope

1. Global Variable
  • Declaring a variable outside the function makes it a Global Variable.
  • Variable is accessed everywhere in the document.

Example : Simple Program on Global Variable

<html>
     <head>
     <script type = "text/javascript">
     count = 5;     //Global variable
     var a = 4;     //Global variable
     function funccount()     // Function Declaration
     {
          count+=5;     // Local variable
          a+=4;
          document.write("<b>Inside function Global Count: </b>"+count+"<br>");
          document.write("<b>Inside function Global A: </b>"+a+"<br>");
     }
     </script>
     </head>
<body>
     <script type="text/javascript">
          document.write("<b>Outside function Global Count: </b>"+count+"<br>");
          document.write("<b>Outside function Global A: </b>"+a+"<br>");
          funccount();
     </script>
</body>
</html>


Output:

Outside function Global Count: 5
Outside function Global A: 4
Inside function Global Count: 10
Inside function Global A: 8

2. Local Variable
  • A variable declared within a function is called as Local Variable.
  • It can be accessed only within the function.

Example : Simple Program on Local Variable

<html>
     <head>
     <script type="text/javascript">
     function funccount(a)     // Function with Argument
     {
          var count=5;     // Local variable
          count+=2;
          document.write("<b>Inside Count: </b>"+count+"<br>");
          a+=3;
          document.write("<b>Inside A: </b>"+a+"<br>");
     }
     </script>
     </head>
<body>
     <script type="text/javascript">
          var a=3, count = 0;
          funccount(a);
          document.write("<b>Outside Count: </b>"+count+"<br>");
          document.write("<b>Outside A: </b>    "+a+"<br>");
     </script>
</body>
</html>


Output:

Inside Count: 7
Inside A: 6
Outside Count: 0
Outside A: 3
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