Question:
In javascript, because there is no declaration of variable types like Integer , String , Boolean , etc., it is a difficult task to know what type of value you are dealing with in a given variable.
So, to make my code consistent, I'd like to know how to go about checking whether a variable is a Numeral or not.
How is this possible?
Answer:
It's simple to know if a variable is Numero or not as there is a native Javascript operator that says the type of your variable, which would be the typeof operator, there are some types of Javascript variables known:
typeof 0; //number
typeof 1; //number
typeof 0.5; //number
typeof '1'; //string
typeof 'a'; //string
typeof " "; //string
typeof true; //boolean
typeof false;//boolean
typeof [1,2] //object
typeof {"obj":[2,3]} //object
typeof {"obj":"3"} //object
typeof function(){alert('foo')} //function
typeof a //undefined -- note que nao declarei a
typeof null //null é um object(wtf)
So here is an example of a function that checks if the type is number
function isNumber(val){
return typeof val === "number"
}
Testing all the values that I exemplified above, you will see that only those with type number that I commented out will return true .
We can also modify "number" by another type to create a function that checks if it's a string for example, or if it's boolean , it's that simple.
In fact, it's a disadvantage, depending on your point of view, that in Javascript you don't need to declare the type and variable before using it.