具体内容如下

先上图：

alert.js代码：

var myAlert = {
 alertbox : function(alertContent){
 var windowWidth = window.innerWidth; 
 windowHeight = window.innerHeight; 
 alertContainer = document.createElement("div");
 alertContainer.id = "myAlertBox";
 alertContainer.style.cssText="position:absolute;left:0px;top:0px;width:100%;z-index:9999;";
 alertContainer.style.height = windowHeight+"px"; 
 alertOpacity = document.createElement("div");
 alertOpacity.style.cssText="position:absolute;left:0px;top:0px;width:100%;background:#000;opacity:0.5;z-index:9999;";
 alertOpacity.style.height = windowHeight+"px"; 
 alertContainer.appendChild(alertOpacity)
 alertMainBox = document.createElement("div");
 alertMainBox.style.cssText="position:absolute;width:200px;height:200px;line-height:200px;text-align:center;background:green;z-index:10000;"
 alertMainBoxLeft = (windowWidth-200)/2;
 alertMainBoxTop = (windowHeight-200)/2;
 alertMainBox.style.left = alertMainBoxLeft+"px";
 alertMainBox.style.top = alertMainBoxTop+"px";
 alertMainBox.innerHTML = alertContent;
 alertContainer.appendChild(alertMainBox);
 alertClose = document.createElement("div");
 alertClose.id = "closeBox";
 alertClose.style.cssText = "position:absolute;right:0px;top:0px;width:30px;height:30px;background:red;cursor:pointer";
 alertMainBox.appendChild(alertClose);
 document.body.appendChild(alertContainer);
 closeButton = document.getElementById("closeBox");
 console.log(closeButton)
 closeButton.onclick = function(){
 document.body.removeChild(document.getElementById("myAlertBox"));
 }
 }
}

以下是具体要用时的代码：

用法很简单，引入alert.js文件，要用时直接myAlert.alertbox("内容");和使用alert一样。