Máscara para formatar telefones em formulários HTML no formato (xx)xxxx-xxxx.

Script:

<script LANGUAGE="JavaScript">
<!-- Begin
var n;
var p;
var p1;
function ValidatePhone(){
p=p1.value
if(p.length==2){
//d10=p.indexOf('(')
pp=p;
d4=p.indexOf('(')
d5=p.indexOf(')')
if(d4==-1){
pp="("+pp;
}
if(d5==-1){
pp=pp+")";
}
//pp="("+pp+")";
document.form1.telefone.value="";
document.form1.telefone.value=pp;
}
if(p.length>2){
d1=p.indexOf('(')
d2=p.indexOf(')')
if(d2==-1){
l30=p.length;
p30=p.substring(0,4);
//alert(p30);
p30=p30+")"
p31=p.substring(4,l30);
pp=p30+p31;
//alert(p31);
document.form1.telefone.value="";
document.form1.telefone.value=pp;
}
}
if(p.length>5){
p11=p.substring(d1+1,d2);
if(p11.length>3){
p12=p11;
l12=p12.length;
l15=p.length
//l12=l12-3
p13=p11.substring(0,3);
p14=p11.substring(3,l12);
p15=p.substring(d2+1,l15);
document.form1.telefone.value="";
pp="("+p13+")"+p14+p15;
document.form1.telefone.value=pp;
//obj1.value="";
//obj1.value=pp;
}
l16=p.length;
p16=p.substring(d2+1,l16);
l17=p16.length;
if(l17>3&&p16.indexOf('-')==-1){
p17=p.substring(d2+1,d2+5);
p18=p.substring(d2+5,l16);
p19=p.substring(0,d2+1);
//alert(p19);
pp=p19+p17+"-"+p18;
document.form1.telefone.value="";
document.form1.telefone.value=pp;
//obj1.value="";
//obj1.value=pp;
}
}
//}
setTimeout(ValidatePhone,100)
}
function getIt(m){
n=m.name;
//p1=document.forms[0].elements[n]
p1=m
ValidatePhone()
}
function testphone(obj1){
p=obj1.value
//alert(p)
p=p.replace("(","")
p=p.replace(")","")
p=p.replace("-","")
p=p.replace("-","")
//alert(isNaN(p))
if(isNaN(p)==true){
alert("Check phone");
return false;
}
}
// End -->
</script>

No formulário, inclua a seguinte função no <input> :

<input type="text" size="20" name="telefone"
value="" onclick="javascript:getIt(this)" maxlength="13">