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Even though it is possible to omit the var keyword from a variable definition, I recommend to
always define your variable with the var keyword:
var apples = 1;
Let’s take a look at some of the basic principles behind variable definitions:
1. A variable is often (but not always) a temporary storage of computer program data.
2. Variables are used to store and manipulate data during program life cycle.
3. The var keyword can be ommited from definition. But doing so is not recommended.
4. The type of a JavaScript variable can be integer, string, boolean, function, array or JSON.
5. In JavaScript a variable is also an object.
6. The variable allocates enough physical computer memory to store the specified value.
Variables are not unique to JavaScript. In other languages variables are created using all kinds
of keywords. In PHP a variable name is prepended a dollar sign as in $apple. In C++, each
different type of a variable has its own keyword. For example int for an integer type, char for
a text character or short for “half ” a variable which is 2 bytes in length. 4 bytes would be a full
32 bit set. On a 64-bit computer processor, an integer is 64-bit long.
In JavaScript we use the var keyword to define a variable of any type. How does JavaScript
determine the type of a variable being created? The type is defined by the assigned value. If we
say that apples = 1, JavaScript automatically creates a variable of type integer.
Determining Variable Type
JavaScript variable definitions are typeless. This means that we can create any type of a variable
and during the program lifecycle we can overwrite it by assigning a new value to it. This new
value doesn’t have to be of the same type as the original. In comparison, this wouldn’t be true
in languages like C++, where a variable of type integer can only be assigned an integer value.
Typeless variables such as ones used by JavaScript can be reassigned, or turned into a different
type using the equal sign. In C++ this process is known as type casting and requires manual
action. But this is completely legal in JavaScript and happens automatically. To check the type
of a variable at any point of its existence, we can use the typeof function:
Parameter Returned result (as string)
typeof(1) “number“
typeof(“hello“) “string”
typeof(true) “boolean”
typeof(object) “object”
typeof(null) “null”
typeof(orange) “undefined” given that the variable named orange does not exist (was never defined)
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