JavaScript实现简单计算器

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>calc</title>
</head>
<body>
<input type="number" name="" id="a_number" value="1">
<select name="yunsuanfu" id="yunsuanfu" >
    <option value="">请选择运算符</option>
    <option value="+" >+</option>
    <option value="-">-</option>
    <option value="*">*</option>
    <option value="/">/</option>
</select>
<input type="number" name="" id="b_number">
的结果是:
<span id="jieguo">【&emsp;】</span>
<br>
<button id="jisuan" onclick="jisuan()">计算</button>
</body>
<script>
function jisuan() {
    var a=  document.getElementById("a_number").value;
    var b=  document.getElementById("b_number").value;
    var yunsuanfu=  document.getElementById("yunsuanfu").value;
    var jieguo ;
    a =  parseFloat(a);
    b =  parseFloat(b);
    if(isNaN(a) || isNaN(b)){
        jieguo="请输入数字";
    }
    if(yunsuanfu===''){
        jieguo="还没有选择运算符"
    }else if(yunsuanfu==='+'){
        jieguo = a+b;
    }else if(yunsuanfu==='-'){
        jieguo = a-b;
    }else if(yunsuanfu==='*'){
        jieguo= a*b;
    }else{
        if(b===0){
            jieguo="除数不能为0"
        }
        jieguo= a/b;
    }
    document.getElementById("jieguo").innerText='【'+ jieguo +'】';
}
</script>
</html>
![简单计算器](https://img.php.cn/upload/image/416/193/351/1637247706719366.png "简单计算器")
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