利用js实现简单计算器

在web二级考试中考到过，印象比较深刻。

HTML部分

<body>
    <link href="jsq.css" rel="stylesheet" type="text/css" />
    <script src="jsq.js" type="text/javascript"></script>
    <div id="calculator">
        <div class="LOGO">
            <span class="name">计算器</span>
        </div>
        <div id="shuRu">
            <!--screen输入栏-->
            <div class="screen">
                <input type="text" id="screenName" name="screenName" class="screen">
            </div>
        </div>
        <div id="keys">
            <!-- j -->
            <!--第一排-->
            <input type="button" id="7" onclick="jsq(this.id)" value="7" class="buttons">
            <input type="button" id="8" onclick="jsq(this.id)" value="8" class="buttons">
            <input type="button" id="9" onclick="jsq(this.id)" value="9" class="buttons">
            <input type="button" id="Back" onclick="tuiGe()" value="Back" class="buttons">
            <input type="button" id="C" onclick="clearNum()" value="C" class="buttons" style="margin-right:0px">
            <!--第二排-->
            <input type="button" id="4" onclick="jsq(this.id)" value="4" class="buttons">
            <input type="button" id="5" onclick="jsq(this.id)" value="5" class="buttons">
            <input type="button" id="6" onclick="jsq(this.id)" value="6" class="buttons">
            <input type="button" id="*" onclick="jsq(this.id)" value="X" class="buttons">
            <input type="button" id="/" onclick="jsq(this.id)" value="/" class="buttons" style="margin-right:0px">
            <!--第三排-->
            <input type="button" id="1" onclick="jsq(this.id)" value="1" class="buttons">
            <input type="button" id="2" onclick="jsq(this.id)" value="2" class="buttons">
            <input type="button" id="3" onclick="jsq(this.id)" value="3" class="buttons">
            <input type="button" id="+" onclick="jsq(this.id)" value="+" class="buttons">
            <input type="button" id="-" onclick="jsq(this.id)" value="-" class="buttons" style="margin-right:0px">
            <!--第四排-->
            <input type="button" id="0" onclick="jsq(this.id)" value="0" class="buttons">
            <input type="button" id="00" onclick="jsq(this.id)" value="00" class="buttons">
            <input type="button" id="." onclick="jsq(this.id)" value="." class="buttons">
            <input type="button" id="%" onclick="jsq(this.id)" value="%" class="buttons">
            <input type="button" id="eva" onclick="eva()" value="=" class="buttons" style="margin-right:0px">
        </div>
        <div class="footer">
            <span class="aside">欢迎使用JavaScript计算器</span>
                <span class="link">
                    <a href="#" title="声明" target="_blank">反馈</a>
                </span>
        </div>
    </div>
    </body>

CSS部分

/*Basic reset*/
*{
    margin:0;
    padding:0;
    box-sizing: border-box;
    font:  14px Arial,sans-serif;
}
html{
    height:100%;
    background-color:lightslategrey;
}

#calculator{
    margin: 15px auto;
    width:330px;
    height:400px;
    border: 1px solid lightgray;
    background-color:darkgrey;
    padding:15px;
}

/*LOGO*/
.LOGO{
    height:20px;

}
.LOGO .name{
    float:left;
    line-height:30px;
}
.LOGO .verson{
    float:right;
    line-height:30px;
}
/*screen*/
#shuRu{
    margin-top:15px;
}
.screen{
    margin-top:5px;
    width:300px;
    height:40px;
    text-align: right;
    padding-right:10px;
    font-size:20px;
}
#keys{
    border:1px solid lightgray;
    height:223px;
    margin-top:25px;
    padding:8px;
}
#keys .last{
    margin-right:0px;
}
.footer{
    margin-top:20px;
    height:20px;
}
.footer .link{
    float:right;
}

#keys .buttons{
    float:left;
    width: 42px;
    height: 36px;
    text-align:center;
    background-color:lightgray;
    margin: 0 17px 20px 0;
}

JS部分

var num = 0;  // 定义第一个输入的数据
        function jsq(num) {
            //获取当前输入
            if(num=="%"){
                document.getElementById('screenName').value=Math.round(document.getElementById('screenName').value)/100;
            }else{
                document.getElementById('screenName').value += document.getElementById(num).value;
            }
        }
        function eva() {
            //计算输入结果
            document.getElementById("screenName").value = eval(document.getElementById("screenName").value);
        }
        function clearNum() {
            //清0
            document.getElementById("screenName").value = null;
            document.getElementById("screenName").focus();
        }
        function tuiGe() {
            //退格
            var arr = document.getElementById("screenName");
            arr.value = arr.value.substring(0, arr.value.length - 1);
        }