JavaScript —— 实现简单计算器【带有 开/关机 清零 退格 功能】

<!doctype html>
<html>
<head>
    <meta charset="utf-8">
    <meta name="keywords" content="Calculator">
    <meta name="description" content="Calculator">
    <meta name="author" content="LIEGE">
    <title>Calculator</title>

<style>

* {
    border: none;
    margin: 0;
    padding: 0;
}
body {

}
.center {
    background-color: #fff;
    border-radius: 50%;
    height: 800px;
    margin: auto;
    width: 800px;
}
h1 {
    color: #495678
    font-size: 30px;
    margin-top: 20px;
    padding-top: 50px;
    display: block;
    text-align: center;
    text-decoration: none;
}

form {
    background-color: #495678;
    box-shadow: 10px 10px #3d4a65;
    margin: 40px auto;
    padding: 40px 0px 30px 30px;
    width: 200px;
}

.btn {
    outline: none;
    font-size: 20px;
    height: 45px;
    margin: 5px 0 5px 10px;
    width: 45px;
}
.btn:first-child {
    margin: 5px 0 5px 10px;
}

#display {
    outline: none;
    background-color: white;
    color: black;
    font-size: 20px;
    height: 47px;
    text-align: right;
    width: 165px;
    padding-right: 10px;
    margin-left: 0px;
}
.btn, #display, form {
    border-radius: 25px;
}

.number {
    background-color: #72778b;
    box-shadow: 0 5px #5f6680;
    color: #dededc;
}
.number:active {
    box-shadow: 0 2px #5f6680;
      -webkit-transform: translateY(2px);
      -ms-transform: translateY(2px);
      -moz-tranform: translateY(2px);
      transform: translateY(2px);
}
.number:hover {
    background-color: rgb(114,119,139,0.4);
    box-shadow: 0 5px #5f6680;
    color: #dededc;
}

.operator {
    background-color: #dededc;
    color: #72778b;
}

.operator:hover {
    background-color:rgb(222,222,220,0.6);
    color: #72778b;
}

.other {
    background-color:rgb(255,0,0,0.7);
    color:#dededc ;
}
.other:hover {
    background-color:rgb(255,0,0,0.4);
    color:#dededc ;
}

.button_clear{
    outline: none;
    border-radius: 25px;
    background-color:#FF4500;
    color:#FFFF00;
    font-size:16px;
    font-style:strong;
    width:40px;
    height:28px;

}
.button_clear:active {
  background-color: red;
  box-shadow: 0 5px #666;
  transform: translateY(2px);
}
.off_on{
    outline: none;
    border-radius: 25px;
    background-color:#FF4500;
    color:#FFFF00;
    font-size:16px;
    font-style:strong;
    width:40px;
    height:28px;
}
.off_on:active{
    background-color: red;
    box-shadow: 0 5px #666;
    transform: translateY(2px);
}
.tishi{
    font-size:10px;
    text-decoration:none;
}
</style>
<script>
var power = 1;
// 1 是开机   -1是关机
function off(){//一开始就运行---》 关机
    power = -power;
    if(power == -1){
        document.getElementById("display").value = "";
    }else{
        welcome();
    }

};
function clearout(){
    if(power == -1){
            document.getElementById("display").value = "";
        }else{
            document.getElementById("display").value = "";
            document.getElementById("display").focus();
        }
};
function welcome(){
    document.getElementById("display").value = "Welcome ☺";
    setTimeout(welcome_end, 2000);
};
function welcome_end(){
    document.getElementById("display").value = "";
    document.getElementById("display").focus();
};

function get(value) {
    if(power == 1){
        document.getElementById("display").value += value;
    }else{
        document.getElementById("display").value = "";
    }

} ;
function back(){
    if(power == 1){
        var now_result = document.getElementById("display"); //*****************************
        document.getElementById("display").value = now_result.value.substring(0, now_result.value.length - 1);
    }else{
        document.getElementById("display").value = "";
    }

};

function calculates() {
    if(power == 1){
        var result = 0;
        result = document.getElementById("display").value;
        document.getElementById("display").value = "";
        document.getElementById("display").value = eval(result);
    }else{
        document.getElementById("display").value = "";
    }

};
function tishi(){
confirm("按钮 C 清零  \n按钮 OFF 开/关机\n按钮 B 退格");
};
</script>
</head>
<body  link="grey" vlink="grey" alink="grey" Onload="off()">
    <div class="center">
        <h1 >Unbrealla™ Calculator <a href="#" onclick="tishi()" class="tishi">HELP</a></h1>
        <form name="calculator">

            <input type="text" id="display" width="300px" value="">
                <br>
                    <br><input type="button" class="button_clear" value="C" onclick="clearout();">
                        <input type="button" class="off_on" value="OFF" onclick="off();">
                        <input type="button" class="off_on" value="B" onclick="back();">
                <br>
            <input type="button" class="btn number" value="1" onclick="get(this.value);">
            <input type="button" class="btn number" value="2" onclick="get(this.value);">
            <input type="button" class="btn number" value="3" onclick="get(this.value);">
            <br />
            <input type="button" class="btn number" value="4" onclick="get(this.value);">
            <input type="button" class="btn number" value="5" onclick="get(this.value);">
            <input type="button" class="btn number" value="6" onclick="get(this.value);">
            <br />
            <input type="button" class="btn number" value="7" onclick="get(this.value);">
            <input type="button" class="btn number" value="8" onclick="get(this.value);">
            <input type="button" class="btn number" value="9" onclick="get(this.value);">
            <br />

            <input type="button" class="btn number" value="0" onclick="get(this.value);">
            <input type="button" class="btn operator" value="-" onclick="get(this.value);">
            <input type="button" class="btn operator" value="+" onclick="get(this.value);">
            <br />

            <input type="button" class="btn operator" value="*" onclick="get(this.value);">
            <input type="button" class="btn operator" value="/" onclick="get(this.value);">
            <input type="button" class="btn other" value="=" onclick="calculates();">
        </form>
    </div>

</body>
</html>