学习js路程记录之简易计算器（eval（））-原创手记-慕课网

这个很简单也没什么技术含量，主要用到的就是js的eval（）；eval() 函数可计算某个字符串，并执行其中的的 JavaScript 代码。我的思路主要是点击输入一个表达式，然后eval这个string，try catch一下；我写的这个兼容性不好，主要是事件对象的获取，在ie中获取不了（window.even获取）我这个直接写了。eval很强大
慢慢学吧。`

<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title></title>
</head>
<style type="text/css">
    .wra {
        width: 300px;
        height: auto;
        overflow: hidden;
        border: 1px solid #D9E400;
        background: #D9E4F1;
    }

    .xian {
        height: 80px;
        background: #ffffff;
        font-size: 30px;
        line-height: 80px;

    }

    .num {
        width: 45px;
        height: 45px;
        float: left;
        margin: 10px;
        line-height: 45px;
        text-align: center;
    }

    .btnli {
        width: 300px;
        float: left;
        display: flex;
        justify-content: center;
        flex-wrap: wrap;
    }
</style>
<body>
<div class="wra">
    <div class="xian" id="xian"></div>
    <div class="btnli" id="btnli" draggable="false">
        <input class="num" type="button" value="1"/>
        <input class="num" type="button" value="2"/>
        <input class="num" type="button" value="3"/>
        <input class="num" type="button" value="+"/>

        <input class="num" type="button" value="4"/>
        <input class="num" type="button" value="5"/>
        <input class="num" type="button" value="6"/>
        <input class="num" type="button" value="-"/>

        <input class="num" type="button" value="7"/>
        <input class="num" type="button" value="8"/>
        <input class="num" type="button" value="9"/>
        <input class="num" type="button" value="*"/>

        <input class="num" type="button" value="0"/>
        <input class="num" type="button" value="."/>
        <input class="num" type="button" value="="/>
        <input class="num" type="button" value="/"/>

    </div>

</div>
</body>
<script type="text/javascript">
    var xian = document.getElementById('xian');
    var nums = document.getElementById('btnli').getElementsByTagName('input');
    for (var i = 0; i < nums.length; i++) {
        if (i == 14) {
            nums[14].onclick = function (even) {
                try {
                    xian.innerHTML = eval(xian.innerHTML);
                } catch (err) {
                    alert('error')
                }
            }
        } else {
            nums[i].onclick = function (even) {
                xian.innerHTML += even.target.value;
            }
        }
    }
    document.onkeydown = function (even) {
        if (xian.innerHTML.length != 0 && even.keyCode == 8) {
            xian.innerHTML = xian.innerHTML.slice(0, xian.innerHTML.length - 1);
        }

    }

</script>
</html>`