邮箱的广泛使用得益于它的免费，因此很多网站在注册的时候都会直接使用邮箱作为账号名
为了提高用户的体验，很多网站都会实现邮箱输入的自动提示功能，所有自己也实现了一个，先看下效果吧，觉得效果还行的就拿去
核心代码（需要jquery的支持）：
(function($){
$.fn.mailAutoComplete = function(options){
var defaults = {
boxClass: "mailListBox", //外部box样式
listClass: "mailListDefault", //默认的列表样式
focusClass: "mailListFocus", //列表选样式中
markCalss: "mailListHlignt", //高亮样式
zIndex: 1,
autoClass: true, //是否使用插件自带class样式
mailArr: ["qq.com","gmail.com","126.com","163.com","hotmail.com","yahoo.com","yahoo.com.cn","live.com","sohu.com","sina.com"], //邮件数组
textHint: false, //文字提示的自动显示与隐藏
hintText: "",
focusColor: "#333"
//blurColor: "#999"
};
var settings = $.extend({}, defaults, options || {});
//页面装载CSS样式
if(settings.autoClass && $("#mailListAppendCss").size() === 0){
$('<style id="mailListAppendCss" type="text/css">.mailListBox{border:1px solid #369; background:#fff; font:12px/20px Arial;}.mailListDefault{padding:0 5px;cursor:pointer;white-space:nowrap;}.mailListFocus{padding:0 5px;cursor:pointer;white-space:nowrap;background:#369;color:white;}.mailListHlignt{color:red;}.mailListFocus .mailListHlignt{color:#fff;}</style>').appendTo($("head"));
}
var cb = settings.boxClass, cl = settings.listClass, cf = settings.focusClass, cm = settings.markCalss; //插件的class变量
var z = settings.zIndex, newArr = mailArr = settings.mailArr, hint = settings.textHint, text = settings.hintText, fc = settings.focusColor, bc = settings.blurColor;
//创建邮件内部列表内容
$.createHtml = function(str, arr, cur){
var mailHtml = "";
if($.isArray(arr)){
$.each(arr, function(i, n){
if(i === cur){
mailHtml += '<div class="mailHover '+cf+'" id="mailList_'+i+'"><span class="'+cm+'">'+str+'</span>@'+arr[i]+'</div>';
}else{
mailHtml += '<div class="mailHover '+cl+'" id="mailList_'+i+'"><span class="'+cm+'">'+str+'</span>@'+arr[i]+'</div>';
}
});
}
return mailHtml;
};
//一些全局变量
var index = -1, s;
$(this).each(function(){
var that = $(this), i = $(".justForJs").size();
if(i > 0){ //只绑定一个文本框
return;
}
var w = that.outerWidth(), h = that.outerHeight(); //获取当前对象（即文本框）的宽高
//样式的初始化
that.wrap('<span style="display:inline-block;position:relative;"></span>')
.before('<div id="mailListBox_'+i+'" class="justForJs '+cb+'" style="min-width:'+w+'px;_width:'+w+'px;position:absolute;left:-6000px;top:'+h+'px;z-index:'+z+';"></div>');
var x = $("#mailListBox_" + i), liveValue; //列表框对象
that.focus(function(){
//父标签的层级
$(this).css("color", fc).parent().css("z-index", z);
//提示文字的显示与隐藏
if(hint && text){
var focus_v = $.trim($(this).val());
if(focus_v === text){
$(this).val("");
}
}
//键盘事件
$(this).keyup(function(e){
s = v = $.trim($(this).val());
if(/@/.test(v)){
s = v.replace(/@.*/, "");
}
if(v.length > 0){
//如果按键是上下键
if(e.keyCode === 38){
//向上
if(index <= 0){
index = newArr.length;
}
index--;
}else if(e.keyCode === 40){
//向下
if(index >= newArr.length - 1){
index = -1;
}
index++;
}else if(e.keyCode === 13){
//回车
if(index > -1 && index < newArr.length){
//如果当前有激活列表
$(this).val($("#mailList_"+index).text());
}
}else{
if(/@/.test(v)){
index = -1;
//获得@后面的值
//s = v.replace(/@.*/, "");
//创建新匹配数组
var site = v.replace(/.*@/, "");
newArr = $.map(mailArr, function(n){
var reg = new RegExp(site);
if(reg.test(n)){
return n;
}
});
}else{
newArr = mailArr;
}
}
x.html($.createHtml(s, newArr, index)).css("left", 0);
if(e.keyCode === 13){
//回车
if(index > -1 && index < newArr.length){
//如果当前有激活列表
x.css("left", "-6000px");
}
}
}else{
x.css("left", "-6000px");
}
}).blur(function(){
if(hint && text){
var blur_v = $.trim($(this).val());
if(blur_v === ""){
$(this).val(text);
}
}
$(this).css("color", bc).unbind("keyup").parent().css("z-index",0);
x.css("left", "-6000px");
});
//鼠标经过列表项事件
//鼠标经过
$(".mailHover").live("mouseover", function(){
index = Number($(this).attr("id").split("_")[1]);
liveValue = $("#mailList_"+index).text();
x.children("." + cf).removeClass(cf).addClass(cl);
$(this).addClass(cf).removeClass(cl);
});
});
x.bind("mousedown", function(){
that.val(liveValue);
});
});
};
})(jQuery);
页面（这里就取一个div做实例）：
<div class="reg_lin1">
<div class="lin1_1">常用邮箱：</div>
<div class="lin1_2"><input type="text" class = "reg_text" id = "email" name = "email"/></div>
<div class="lin1_3"></div>
</div>
<script type="text/javascript">
$("#email").mailAutoComplete({
boxClass: "out_box", //外部box样式
listClass: "list_box", //默认的列表样式
focusClass: "focus_box", //列表选样式中
markCalss: "mark_box", //高亮样式
autoClass: false,
textHint: true //提示文字自动隐藏
});
</script>
还有点css，这个可能需要大家自己修改成自己想要的色调
<!-- 邮箱自动提示的css -->
<style type="text/css">
.out_box{border:1px solid #ccc; background:#fff; font:12px/20px Tahoma;}
.list_box{border-bottom:1px solid #eee; padding:0 5px; cursor:pointer;}
.focus_box{background:#f0f3f9;}
.mark_box{color:#c00;}
</style>