效果图：
源代码：
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title></title>
<style type="text/css">
* {
margin: 0;
padding: 0;
}
.dome {
width: 400px;
height: 430px;
margin: 50px auto;
background: #CCC;
padding: 20px;
}
.dome>input {
width: 100%;
height: 50px;
font-size: 24px;
margin-bottom: 30px;
}
.dome>button {
width: 90px;
height: 60px;
background-color: white;
border: none;
margin: 5px;
float: left;
font-size: 18px;
}
button:hover {
cursor: pointer;
}
</style>
</head>
<body>
<div class="dome">
<!-- disabled="disabled" 禁用输入框 -->
<input type="" name="" id="ipt" value="0" />
<button class="num">7</button>
<button class="num">8</button>
<button class="num">9</button>
<button id="del">←</button>
<button class="num">4</button>
<button class="num">5</button>
<button class="num">6</button>
<button class="ysf">+</button>
<button class="num">1</button>
<button class="num">2</button>
<button class="num">3</button>
<button class="ysf">-</button>
<button>%</button>
<button class="num">0</button>
<button class="num">.</button>
<button class="ysf">*</button>
<button id="clear">AC</button>
<button class="ysf">/</button>
<button id="result" style="width: 190px; background-color: #333; color: white;">=</button>
</div>
</body>
</html>
<script type="text/javascript">
//1.把数字和小数点归为一类。class="num"
//2.把加减乘除运算符归为一类。
//3.显示框，退格键，归零键，等号 单独设置id。
//4.把显示框，归零键，等号，退格 标签对象获取出来。
//5.点击数字，在显示框上显示
//6.要做运算，条件得两个数和一个运算符
//7.定义三个变量用来接收第一个数，第二个数和运算符。
//8.四则运算
var numValue1 = '';
var numValue2 = '';
var czf = '';
var ipt = document.getElementById("ipt");
var del = document.getElementById("del");
var clear = document.getElementById("clear");
var result = document.getElementById("result");
var numArr = document.getElementsByClassName("num");
for (var i = 0; i < numArr.length; i++) {
//给每个数字绑定单击事件
numArr[i].onclick = function() {
//判断用户是否在输入小数点
if(this.innerText=="."){
//alert("点小数点了");
if(numValue1.indexOf(".")==-1&&numValue1.length>=1){
// var num = this.innerText;
// alert(num);
numValue1 += this.innerText;
//乘1会去掉首尾无效的0
ipt.value = numValue1*1;
}
}else{
// var num = this.innerText;
// alert(num);
numValue1 += this.innerText*1;
//乘1会去掉首尾无效的0
ipt.value = numValue1;
}
}
}
//给运算符绑定单击事件
var ysfArr = document.getElementsByClassName("ysf");
for (var i = 0; i < ysfArr.length; i++) {
//给每个数字绑定单击事件
ysfArr[i].onclick = function() {
//当用户点击了运算符，把第一个数字给第二个数字，然后把第一个数字清空，用来接收用户输入的第二个数字
//alert(this.innerText);
if (numValue2 == '') {
numValue2 = numValue1;
numValue1 = '';
czf = this.innerText;
//alert("普通运算");
} else {
//有可能会进行四则运算
//alert("有可能会进行四则运算");
if(numValue1!=''){
resultFun();
}
}
//保存操作符
czf = this.innerText;
}
}
//给等号绑定单击事件，进行运算
result.onclick = function() {
resultFun();
}
//运算结果
function resultFun() {
var one = Number(numValue2);
var two = Number(numValue1);
var r = null;
switch (czf) {
case '+':
r = one + two;
break;
case '-':
r = one - two;
break;
case '*':
r = one * two;
break;
case '/':
if (two == 0) {
alert("除数不能为0");
numValue1 = '';
numValue2 = '';
czf = '';
r = 0;
} else {
r = one / two;
}
break;
}
//四则运算时，把上一次运算的结果给numValue2，然后把numValue1 清空
numValue2 = new Number(r).toFixed(4)*1;
numValue1='';
ipt.value = numValue2;
}
//归零键
clear.onclick = function() {
numValue1 = '';
numValue2 = '';
czf = '';
ipt.value = '0';
}
//退格键
del.onclick = function() {
if (numValue1.length >= 1) {
numValue1 = numValue1.substring(0, numValue1.length - 1);
ipt.value = numValue1;
}else if(numValue2.length >= 1){
numValue2 = numValue2.substring(0, numValue2.length - 1);
ipt.value = numValue2;
}else {
numValue1 = '';
numValue2 = '';
czf = '';
ipt.value = '0';
}
}
</script>补充说明：仍有部分bug尚未解决，因作者水平有限，代码仅供参考。
