1//typeof() will return the type of value in its parameters.
2//some examples of types: undefined, NaN, number, string, object, array
3
4//example of a practical usage
5if (typeof(value) !== "undefined") {//also, make sure that the type name is a string
6  	//execute code
7}

1console.log(typeof 93);
2// Output = "number"
3
4console.log(typeof 'Maximum');
5// Output = 'string'
6
7console.log(typeof false);
8// Output = "boolean"
9
10console.log(typeof anUndeclaredVariable);
11// Output = "undefined"

1var obj = new String();
2var str = "this is string";
3            
4typeof obj; // returns object
5typeof str; // returns string
6
7