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    VARIABLES
                      A variable is a memory reference to a stored value. It is used to name any data so that it can be

                      accessed later in the script. Variables can be declared and initialised in a script as follows:
                          let: It declares a variable that can be changed later. It’s limited to the block it’s in (like a loop
                         or function).

                         let x = 5; // Here, you can change the value of variable x.

                        x = 10;
                          var: It declares a variable that can be changed and redeclared. It works globally or within a
                         function, but it’s less commonly used now.

                         var y = 20;

                        var y = 30;  // You can redeclare it.

                         Here, you can redeclare the value of variable y.
                          const: It declares a constant that can’t be changed. Once a value is set, it stays the same.

                         const z = 15;

                        z = 20;  // Error! You can't change a const value.
                         Here, the error occurs. You cannot change the value of a const variable.

                      When naming variables, the following rules must be followed:
                          A variable can contain letters, numbers, dollar signs ($) and underscores (_).

                          Spaces are not allowed in variable names.
                          JavaScript keywords cannot be used as variable names.

                           A variable name cannot start with a numeral (0-9). It must begin with a letter or an underscore.
                         For example, 123test is invalid, but _123test is valid.
                          Variable names are case-sensitive. For example, Name and name are different variables.

                          Variable names must be shorter than 255 characters.

                         Code
                           3       Create a web page to demonstrate the use of variables in JavaScript.

                      <!DOCTYPE HTML>

                      <HTML>

                      <HEAD>
                      <TITLE>Variables</TITLE>

                      </HEAD>
                      <BODY>

                      <SCRIPT>

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