Form validation with index()

Question

I know you can validate with HTML5 or CSS, but just out of curiosity: I found a code on the net that checks if the syntax of a typed email is correct:

if(document.dados.email.value=="" || document.dados.email.value.indexOf('@') == -1 || document.dados.email.value.indexOf('.')  == -1 ) 
        { 

And it works. The problem is that I cannot understand how this conditional value "-1" can be legitimate if there is no negative array or string value.

However basing myself on a thread of logic I assumed that "-1" meant "not to exist", hence I modified this to <0 and then to <1 and the two also worked.

Could you please give me a clearer explanation of this case?

Answer 1

The indexOf() exists for Arrays and Strings, works basically the same way:

_{(Note that the Arrays method is newer and only available on IE9+)}

• -1 if there is no array or string for the searched value
• of 0 and forward is for case it exists and then the number is the position of the element in the String and Array

In your case, when you have document.dados.email.value.indexOf('@') == -1 this check gives true if there is no arroba (@) in String.

In the case of document.dados.email.value.indexOf('@') give away 0 validation should fail because this would be an email like @gmail.com without "username", so your idea to check with < 1 makes a lot of sense.