Variables are containers that stores values of various data type. A variable has a name and a value.
|Reserved and Keywords
A variable starts with the keyword var followed by the name of the variable and ends with a semi-colon. It is helpful to declare variables with meaningful names.
You can declare more then one variable in a single line followed by a comma after each name and end it with a semi-colon.
Once a variable has been declared you have to initialise it in other words assign a value. The equal sign is used to assign the value.
The values of a variable can change from a number to a string. If you are going to declare a variable that
holds numbers then stick to numbers. Otherwise, your codes could get messy.
Let us declare a variable age as a number and then change the variable age to a string.
The keyword const is used instead of var, so the variable value remains constantly the same through out the program.
Let's write a program that finds the area of a circle. We want the value of pi to be constant, so the keyword const will be used instead of var.
There are functions, which you can use to convert the value of a string to a number or vice versa.
The parseInt() functions lets you convert a string to an integer. The value of the string conversion must be inside the parseInt parentheses with quotation marks.
The parseFloat() converts a string to a decimal number.
There are two variable scopes local and global.
If you assign a variable outside a function it is called a global variable. It can be accessed by any of the functions on that page.
If you assign a variable inside a function it is called a local variable. It can only be accessed by that particular function.
However, if you declare a variable inside a function without the keyword var then it becomes a global variable.
In the example below we have declared two global variables a and b and have assigned the values 10 and 12. Inside the function we have declared a variable called answer, which has not been assigned a value.
However, when the function addition() is called the the value of answer will be the sum of a and b.