regular expression for mobile no. length must be 10 in js

var phoneno = /^\(?([0-9]{3})\)?[-. ]?([0-9]{3})[-. ]?([0-9]{4})$/;  
    if(inputtxt.value.match(phoneno))  
    {  
        return true;  
    }  
    else  
    {  
        alert("message");  
        return false;  
    }