console 命令行工具 X clear

console

 function alertSecond(){
     alert("第2次");
 }

function changeColor() {
    if (this.style.color == "red") {
        this.style.color = "black";
    }
    else {
         this.style.color = "red";
    }  
}

function changeBackgroundColor() {
    if (this.style.backgroundColor == "lightskyblue") {
        this.style.backgroundColor = "white";
    }
    else {
         this.style.backgroundColor = "lightskyblue";
    } 
} 

 window.onload = function () 
        {
            //事件处理器和事件监听器
            var oBtn = document.getElementById("btn");
            oBtn.onclick = function () {
                alert("第1次");
            };
            oBtn.onclick = function () {
                alert("第2次");
            };
            oBtn.onclick = function () {
                alert("第1次");
                alert("第2次");
                alert("第3次");
            };       

        var oBtn = document.getElementById("listenBtn");

        oBtn.addEventListener("click",function(){
            alert("第1次");
        } ,false);
        oBtn.addEventListener("click",alertSecond,false);
        oBtn.removeEventListener("click",alertSecond,false);

        var oPContent = document.getElementById("content");
        oPContent.addEventListener("click",changeColor,false);
        oPContent.addEventListener("click",changeBackgroundColor,false);

        var oBtn = document.getElementById("removeBtn");

        oBtn.addEventListener("click",function(){
            oPContent.removeEventListener("click",changeColor,false);
        } ,false);


        var oPContent1 = document.getElementById("content1");
        oPContent1.onclick = changeColor;

        var oBtn1 = document.getElementById("removeBtn1");

        oBtn1.addEventListener("click",function(){
            oPContent1.onclick = null;
        } ,false);

}

<!DOCTYPE html> 
<html>
<head>
    <meta charset="utf-8" />
    <title></title>
    <script>
      
    </script>
</head>
<body>
    <input id="btn" type="button" value="按钮"/>
    <br/><br/>
    <input id="listenBtn" type="button" value="监听按钮"/>
    
    <div>
        <p id="content">广州新华学院</p>
        <button id="removeBtn">解除</button>
    </div>
     <div>
        <p id="content1">信息科学学院</p>
        <button id="removeBtn1">解除</button>
    </div> 
</body>
</html>