JS 实现计算器功能

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<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>计算器</title>
    <style>
        body,p,input,ul,li,div{
            margin: 0;
            padding: 0;
        }
        #calc{
            position: relative;
            border-radius: 10px;
            margin: 0 auto;
            width: 400px;
            height: 500px;
            background: #ccc;
        }
        p{
            text-align: center;
        }
        .f-text{
            padding-top: 10px;
           box-sizing: border-box;
           border: 0;
            margin: 0 auto;
            font-size: 30px;

            text-align: right;
            width: 400px;
            height: 60px;
        }
        ul{
            list-style-type: none;

        }
        ul li{

            float: left;
            width: 90px;
            height: 50px;
            margin: 25px 10px 0 0;
            font-size: 30px;
            font-family: Arial, Helvetica, sans-serif;

        }
        ul li a{
            margin: 0 auto;
            display: block;
            width: 60px;
            height: 60px;
            line-height: 50px;
            box-sizing: border-box;
            border-radius: 10px;
            box-shadow: white;
            text-align: center;
            text-decoration: none;
            color: white;
            background: black;
        }
        ul li a:hover{
            cursor: pointer;
            color: saddlebrown;
        }
        #formula{
            margin-left: -400px;
            box-sizing: border-box;
            border: 0;
            margin-top: -60px;
            position: absolute;
            width: 400px;
            height: 20px;
        }
    </style>
</head>
<body>
   <div id="calc">
       <p>简易计算器</p>
        <input class="f-text" type="text" readonly="readonly" maxlength="9" value="0" />

            <ul>
                <li class="btn-1"><a href="javascript:void(0)">c</a></li>
                <li class="btn-1"><a href="javascript:void(0)">%</a></li>
                <li class="btn-1"><a href="javascript:void(0)">/</a></li>
                <li class="btn-1"><a href="javascript:void(0)">x</a></li>
                <li><a href="javascript:void(0)">7</a></li>
                <li><a href="javascript:void(0)">8</a></li>
                <li><a href="javascript:void(0)">9</a></li>
                <li class="btn-1"><a href="javascript:void(0)">-</a></li>
                <li><a href="javascript:void(0)">4</a></li>
                <li><a href="javascript:void(0)">5</a></li>
                <li><a href="javascript:void(0)">6</a></li>
                <li class="btn-1"><a href="javascript:void(0)">+</a></li>
                <li><a href="javascript:void(0)">1</a></li>
                <li><a href="javascript:void(0)">2</a></li>
                <li><a href="javascript:void(0)">3</a></li>
                <li class="btn-2"><a href="javascript:void(0)">=</a></li>
                <li class="btn-3"><a href="javascript:void(0)">0</a></li>
                <li><a href="javascript:void(0)">.</a></li>
                <li><a href="javascript:void(0)">(</a></li>
                <li><a href="javascript:void(0)">)</a></li>
            </ul>
        <input id="formula" type="text" readonly="readonly" value=""/>
   </div>
</body>
</html>
<script>
    var calc=document.getElementById("calc");
    var a=calc.getElementsByTagName("a");
    var input=calc.getElementsByTagName("input")[0];
    var formula=document.getElementById("formula");
    var s=false;
    var i;

    for(i=0;i<a.length;i++){
        a[i].onfocus=function(){
            this.blur()
        };
        a[i].onclick=function(){
            switch(this.innerHTML){
                case "c":
                input.value=0;
                formula.value="";
                break;
                case "%":
                count("%")
                break;
                case "x":
                count("*")
                break;
                case "-":
                count("-")
                break;
                case "+":
                count("+")
                break;
                case "(":
                count("(")
                break;
                case ")":
                count(")")
                break;
                case "=":
                s || (formula.value+=input.value);

                input.value=eval(formula.value.replace(/\%\/\*\-\+/,''));//输入的值进行运算后得到的值

                input.value=input.value.substr(0,10).replace("NaN",0);//计算输入变量和输出结果最多前10位,如果不是数字返回0

                s=true;
                break;
                case ".":
                if(input.value.search(/[\.\%\/\*\-\+]/)!=-1)//输入的值为非运算符时

                break;
                default:
                s && (input.value=0,formula.value="",s=false);
                input.value.length<10 &&(input.value=(input.value+this.innerHTML).replace(/^[0\%\/\*\-\+](\d)/,"$1"));

            }
        }
    }
    function count(d){

       var reg = /[\%\/\*\-\+]$/;
        if(s)
        {   //错误处理
            formula.value=input.value + d;
            input.value=d;
            s=false;
        }
        else
        {   //正确处理
            reg.test(input.value) || (formula.value+=input.value);
            console.log('3',/[\%\/\*\-\+]$/.test(input.value));

            input.value=d;
            console.log("n",input.value);
            reg.test(formula.value) || (formula.value+=input.value);
            formula.value=formula.value.slice(-1)!=d ? formula.value.replace(/.$/,d):formula.value
       }
    }
</script>

  

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