help: validation of input type text for telephone number

Hi people!
I’m sorry for my bad english, please answer me in simple words.

I’m trying to validate an input type text html tag with JS.

There is an array (prefisso[]) with a lot of dial codes.
The first 3 characters of the value to check must be one of the elements of “prefisso[]”.
The value to check must be longer than 9 chars (min 10).

Were I’m wrong?

thank you!

[CODE]
function verifytel(elem) {
var prefisso=new Array();

prefisso[0]=”331″;
// …
// FOLLOWS A LOT OF DIAL CODES
// …
prefisso[36]=”377″;
prefisso[37]=”331″;
prefisso[38]=”377″;

var check=false;
if(!isNaN(elem.value)) {
if((elem.value.length>=10)) {
for(var i=0; i<prefisso.length; i++) {
if(elem.value.startsWith(prefisso[i])==true) {
check=true;
elem.style.backgroundColor=”#00ff00″;
}
}
if(check==false) alert(“Invalid telephone number.”);
}
}
else alert(“Please insert only numbers, no dots, blank spaces, etc.”);
}[/CODE]

Also in #JavaScript _↴