var wait=60;

function time(o) {

        if (wait == 0) {

            o.removeAttribute("disabled");

            o.value="免费获取验证码";

            wait = 60;

        } else {

            o.setAttribute("disabled", true);

            o.value="重新发送(" + wait + ")";

            wait--;

            setTimeout(function() {

                time(o)

            },

            1000)

        }

    }

document.getElementById("btn").onclick=function(){time(this);}