https://speedio.com.br/obrigadoo/js/validacao-form.js

1function validateform() {
2    var stakeholder_full_name = document.leadformulario.stakeholder_full_name.value;
3    var x = document.leadformulario.stakeholder_contact_email.value;
4    var atposition = x.indexOf("@");
5    var dotposition = x.lastIndexOf(".");
6    if (stakeholder_full_name == null || stakeholder_full_name == "") {
7        document.getElementById("nomeloc").innerHTML = "Informe o nome da empresa";
8        return false;
9    }
10    if (atposition < 1 || dotposition < atposition + 2 || dotposition + 2 >= x.length) {
11        document.getElementById("emailloc").innerHTML = "Informe um e-mail válido";
12        return false;
13    }
14}
15
16/* Máscaras ER */
17function mascaraFone(event) {
18    var valor = document.getElementById("telefone").attributes[0].ownerElement['value'];
19    var retorno = valor.replace(/\D/g, "");
20    retorno = retorno.replace(/^0/, "");
21    if (retorno.length > 10) {
22        retorno = retorno.replace(/^(\d\d)(\d{5})(\d{4}).*/, "($1) $2-$3");
23    } else if (retorno.length > 5) {
24        if (retorno.length == 6 && event.code == "Backspace") {
25            return;
26        }
27        retorno = retorno.replace(/^(\d\d)(\d{4})(\d{0,4}).*/, "($1) $2-$3");
28    } else if (retorno.length > 2) {
29        retorno = retorno.replace(/^(\d\d)(\d{0,5})/, "($1) $2");
30    } else {
31        if (retorno.length != 0) {
32            retorno = retorno.replace(/^(\d*)/, "($1");
33        }
34    }
35    document.getElementById("telefone").attributes[0].ownerElement['value'] = retorno;
36}