Maybe pretty easy question.
Where should I use var keyword in JavaScript. It seems to me using it or not have the same effect ( but of course I'm still learning the language )
For instance these both seems the same to me:
(function(){
var a = "mundo"
alert("Hola, " + a )
})()
and
(function(){
a = "mundo"
alert("Hola, " + a )
})()
But of course there must be a more complex example where the difference shows up.
Answer
When you use var , you are instantiating a variable in the current scope. This will also prevent access of variables named the same in higher scope, within the current scope.
In your first example, 'a' is being instantiated and set within the function scope. In your second example, 'a' is being set outside the function scope due to lack of var
With var:
var a = "A"
(function(){
var a = "B"
alert(a) //B
})()
alert(a); //A
Without var:
var a = "A";
(function(){
a = "B"
alert(a) //B
})()
alert(a) //B