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window.addEventListener("load",function()
{
    var oOpenBaiduBtn = this.document.getElementById("openBaiduBtn");
    var oBaiduWin = null;
    oOpenBaiduBtn.addEventListener("click",function()
    {
        oBaiduWin = window.open("https://www.baidu.com/?tn=15007414_8_dg","_blank");
    });

    var oCloseBaiduBtn = this.document.getElementById("closeBaiduBtn");
    oCloseBaiduBtn.addEventListener("click",function()
    {
        oBaiduWin.close();
    });


    var oOpenNewBtn = this.document.getElementById("openNewBtn");
    var oNewWin = null;
    oOpenNewBtn.addEventListener("click",function()
    {
        oNewWin = window.open();
    });

    var oChangeNewBtn = this.document.getElementById("changeNewBtn");
    oChangeNewBtn.addEventListener("click",function()
    {
        oNewWin.document.title = "新窗口";
        oNewWin.document.body.innerHTML = "<div><p><strong>Hi</strong>,I'm a new window</p></div>";
        oNewWin.document.body.style.color = "blue";
    });

    var oCloseNewBtn = this.document.getElementById("closeNewBtn");
    oCloseNewBtn.addEventListener("click",function()
    {
        oNewWin.close();
    });


    var oAlertBtn = this.document.getElementById("alertBtn");
    oAlertBtn.addEventListener("click",function()
    {
        window.alert("我是告警窗口");
    });

    var oConfirmBtn = this.document.getElementById("confirmBtn");
    oConfirmBtn.addEventListener("click",function()
    {
        var bConfirmed = window.confirm("你要不要打开百度？");
        if(bConfirmed)
        {
            window.open("https://www.baidu.com/?tn=15007414_8_dg");
        }
    });

    var oPromptBtn = this.document.getElementById("promptBtn");
    oPromptBtn.addEventListener("click",function()
    {
        var strText=window.prompt("请输入提示：");
        if(strText){
            var oText=window.document.getElementById("text");
            oText.innerHTML=strText;
        }
    });


    //定时器
    //1、setTimeout与clearTimeout
    var ostartTimerBtn = this.document.getElementById("startTimer");
    var ostopTimerBtn = this.document.getElementById("stopTimer");
    var oTimerBox = this.document.getElementById("timerBox");
    var oTimer;

    ostartTimerBtn.addEventListener("click",function()
    {
        if(oTimer)
        {
            window.clearTimeout(oTimer);
        }
        oTimer = window.setTimeout(function()
        {
            oTimerBox.style.backgroundColor = "blue";
        },2000);
    });

   
    ostopTimerBtn.addEventListener("click",function()
    {
        if(oTimer)
        {
            window.clearTimeout(oTimer);
        }
    });

    //2、
    var ostartIntervalBtn = this.document.getElementById("startInterval");
    var ostopIntervalrBtn = this.document.getElementById("stopInterval");
    var oIntervalBox = this.document.getElementById("intervalBox");
    var oIntervalText = this.document.getElementById("intervalText");
    var oInterval;
    var count = 5;

    function changeColor()
    {
        var colors=["red","yellow","blue","green","pink"];
        if(count>0)
        {
            count--;
            oIntervalBox.style.backgroundColor= colors[count];
            oIntervalText.innerHTML = count;
        }
        else
        {
            count=5;
        }
    }
    ostartIntervalBtn.addEventListener("click",function()
    {
        if(oInterval)
        {
            window.clearInterval(oInterval);
        }
        oInterval = window.setInterval(changeColor,1000);
    });

    ostopIntervalrBtn.addEventListener("click",function()
    {
        if(oInterval)
        {
            window.clearInterval(oInterval);
        }
    });


})

<!DOCTYPE html> 
<html>
<head>
    <meta charset="utf-8" />
    <title></title>
    <script>
    </script>
</head>
<body>
    <div>
        <button id="openBaiduBtn">打开百度</button>
        <button id="closeBaiduBtn">关闭百度</button>
    </div>
    <br/>
    <div>
        <button id="openNewBtn">打开空白页面</button>
        <button id="changeNewBtn">绘制空白页面</button>
        <button id="closeNewBtn">关闭空白页面</button>
    </div>
    <br/>
    <div>
        <button id="alertBtn">打开告警窗口</button>
        <button id="confirmBtn">打开确认窗口</button>
        <br/>
        <div>
            <button id="promptBtn">打开提示窗口</button>
            <label>提示文字:</label><p id="text"></p>
        </div>
    </div>

     <br/>
    <div>
        <button id = "startTimer">开始</button>
        <button id = "stopTimer">结束</button>
        <div id="timerBox"></div>
    </div>
    <br/>
    <div>
        <button id = "startInterval">开始</button>
        <button id = "stopInterval">结束</button>
        <div id="intervalBox"></div>
        <span>倒计时：</span><span id="intervalText"></span>
    </div> 
</body>
</html>

#timerBox {
    width: 100px;
    height: 100px;
    border : 1px solid black;
    background-color: lightblue;
}

#intervalBox {
    width: 100px;
    height: 100px;
    border : 1px solid black;
    background-color:blueviolet;
}