原生js实现ajax用于简单的签到或登录

<script>
function createStandardXHR() {
    try {
        return new window.XMLHttpRequest();
    } catch( e ) {}
}
function createActiveXHR() {
    try {
        return new window.ActiveXObject( "Microsoft.XMLHTTP" );
    } catch( e ) {}
}
function getXhr() {
    var xhr = window.ActiveXObject !== undefined ?
    // Support: IE6+
    function() {
        return createStandardXHR() || createActiveXHR();
    } :
    // For all other browsers, use the standard XMLHttpRequest object
    createStandardXHR;
    return xhr;
}
function get(url, callback){ 
    var req = getXhr()();
    if(req){ 
        req.open("GET", url, true); 
        req.onreadystatechange = function(){ 
            if(req.readyState == 4){ 
                if(req.status == 200){ 
                    callback(req.responseText);
                }else{ 
                    alert("error"); 
                } 
            } 
        } 
        req.send(null); 
    } 
}
    !(function(win, document){
        var ipt_email = document.getElementById('ipt_email');
        ipt_email.onfocus = function(){
            this.value = '';
        };
        var ipt_sub = document.getElementById('ipt_sub');
        var tot_email = document.getElementById('tot_email');
        ipt_sub.onclick = function(){
            var val = ipt_email.value;
            if(/\w/.test(val)){
                var url = 'index.php?email_prefix=' + val;
                get(url,function(data){
                    if ('1' === data) {
                        alert('签到成功！欢迎出席搜房十六周年庆典暨扩大管理会议！');
                    } else if ('2' === data) {
                        alert('对不起，您已经签到过！');
                    } else if ('3' === data) {
                        alert("对不起，还未到签到时间，请耐心等待！");
                    } else {
                        alert('对不起，未能匹配到您的信息，请核对邮箱！');
                    }
                });
            }else{
                tot_email.getElementsByTagName('p')[0].innerHTML = '请正确输入邮箱地址！';
            }
        };
    })(window, document)
    </script>

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