THE BASICS ON JavaScript ~ Mahesh Prashad Joshi

DECLARATION AND INITIALIZATION

As we discussed introductions and some main important of JavaScript in programming word for beginners. Now in second lecture we are discussing about some new points like basics in JavaScript , declaration on JavaScript etc.

Before we use a variable in a JavaScript program, we must declare it. Variables are declared with the var keyword. For example:

                                                             var age;

var name;

And also we can use only keyword for more variables as:

                                                              var age, name;

Storing a value in a variable is called variable initialization. We can do variable initialization at the time of variable creation or at a later point in time when we need that variable.

For instance, we might create a variable named money and assign the value 24 to it later. For another variable, we can assign a value at the time of initialization as follows:

                     var name = "Mahesh Prashad Joshi";

                var age;

                     age = 24;

We should remember that the var keyword only for declaration or initialization, once for the life of any variable name in a document. We should not re-declare same variable twice.

If we are declaring the variable in JavaScript we should use the variables properly. For example:

These declarations will so the result as:

If we interchange the declaration steps in another way like:

alert(x);

x="Mahesh Prashad Joshi"

var x;

</script>

This result as:

Reference Error and Undefined Basically we may face two kinds of errors Reference while declaration of the variable. Reference error arises if we have not declared a variable but we are trying to use it. Undefined is the case when we try to use a variable that we have declared but have not assigned any value to it.

document.writeln(x);

</script>

This shows the reference error while run in the browser as shown as below:

And lets see another error:

This declaration creates the undefined type of error in JavaScript. And shows the result as:

Data Types in JavaScript:

Basically JS has 8 basic data types:

SN	Data Type	Work As
1	number	variable with number data type stores integer or floating-point values.
2	bigint	integer numbers(of arbitrary length).
3	string	For string values.
4	boolean	True/false.
5	null	Unknown values
6	undefined	Unassigned value.
7	object	Complex data structures.
8	symbol	Unique Identifier.