JS入门第一节

<!DOCTYPE>
<html>
<head>
    <!--注意两个标签之间不能有任何内容,否则会导致页面失效-->
    <script src="my.js"></script>
</head>
<body>
    <!--行内JS-->
    <button onclick="alert('努力,奋斗')">点击触发页面弹窗</button>

    <!--内部JS一般放在body内部的末尾,因为会影响后面其他类型标签的渲染-->
    <!--script 标签是按照出现的位置执行的-->
    <script>
        alert('努力,奋斗');
    </script>
</body>
</html>
<!--外部 js 文件-->
alert('努力,奋斗')

<script>
	alert('你好 JS~')
	document.write('JavaScript 我来了!')
	console.log('它~会魔法吧~')
</script>

<script>
        let num = 20;
        let uname = '张三';
        console.log(`num = ${num}, uname = ${uname}`);
</script>

<script>
        let name;
        name = prompt('请输入姓名:');
        document.write('您的姓名为: ' + name);
</script>

<script>
        let num1 = 10;
        let num2 = 20;
        let temp = num1;
        num1 = num2;
        num2 = temp;

        document.write(`num1 = ${num1}, num2 = ${num2}`);
</script>

<script>
        let uname, age, gender;
        uname = prompt('请输入您的姓名:');
        age = prompt('请输入您的年龄:');
        gender = prompt('请输入您的性别:');

        document.write(`uname = ${uname}, age = ${age}, gender = ${gender}`);
</script>

<script>
        let week = [
            '星期一',
            '星期二',
            '星期三',
            '星期四',
            '星期五',
            '星期六',
            '星期日',
        ]

        document.write(week[6]);
</script>

<script>
        const pi = 3.14;
        let area;
        let r = prompt('请输入半径');
        are = pi * r * r;
        document.write('圆的面积为:'+area);
</script>

<script>
        let uname, age;
        uname = prompt('请您输入姓名');
        age = prompt('请您输入年龄');
        document.write(`大家好,我叫${uname},今年${age}岁了`);
</script>

<script>
        let num1, num2;
        num1 = prompt('请输入第一个数');
        num2 = prompt('请输入第二个数');
        document.write(`sum = ${Number(num1) + parseInt(num2)}`);
</script>

<script>
        let price, num, address;
        price = prompt('请输入商品价格:');
        num = prompt('请输入商品数量:');
        address = prompt('请输入收货地址:');

        document.write(`price = ${price}, num = ${num}, address = ${address}`);
</script>

<!DOCTYPE>
<html>
<head>
    <style>
        h2 {
          text-align: center;
        }
    
        table {
          /* 合并相邻边框 */
          border-collapse: collapse;
          height: 80px;
          margin: 0 auto;
          text-align: center;
        }
    
        th {
          padding: 5px 30px;
        }
    
        table,
        th,
        td {
          border: 1px solid #000;
        }
      </style>
</head>
<body>
    
    

    <h2>订单确认</h2>
    <script>     
        let price, num, address;  
        price = prompt('请输入商品价格:');
        num = prompt('请输入商品数量:');
        address = prompt('请输入收货地址:');
        let sum = price * num;

        document.write(`
            
            <table>
                <tr>
                    <th>商品名称</th>
                    <th>商品价格</th>
                    <th>商品数量</th>
                    <th>总价</th>
                    <th>收货地址</th>
                </tr>
                <tr>                   
                    <td>小米手机青春PLUS</td>
                    <td>${price}元</td>
                    <td>${num}</td>
                    <td>${sum}元</td>
                    <td>${address}</td>
                </tr>
            </table>
        `);
    </script>  
</body>
</html>

📖 补充

    <script>
    /*
        string、string1、NAN、pink1
        如果一个只要有一个字符串的+运算,作用就是拼接 [如果+位于字符串前,作用是将字符串转为数字]
        其他运算符 - * / % 会将式子转为数学运算
        typeof 运算符的优先级更高
    */
    console.log(typeof "1")
    console.log(typeof '1' + 1)
    console.log('1' - 1)
    console.log('pink' + 1)
</script>

<script>
        let number = prompt('请输入一个数:');
        if(number % 4 === 0 && number % 100 !== 0){
            alert(true);
        }else{
            alert(false);
        }
</script>

<script>
        let a = 3 > 5 && 2 < 7 && 3 == 4
        console.log(a);
        let b = 3 <= 4 || 3 > 1 || 3 != 2
        console.log(b);
        let c = 2 === "2"
        console.log(c);
        let d = !c || b && a
        console.log(d);
        // false、true、false、true

</script>

<script>
        let score = prompt('请输入您的高考成绩:')
        if(score > 700){
            alert('恭喜考入黑马程序员')
        }
</script>

<script>
        let uname = prompt('请输入用户名:');
        let password = prompt('请输入密码:');
        if(uname === 'pink' && password === '123456'){
            alert('登录成功');
        }else{
            alert('登录失败');
        }
</script>

<script>
        let year = prompt('请输入年份:');
        if((year % 4 === 0 && year % 100 !== 0) || (year % 400 === 0)){
            alert('闰年');
        }else{
            alert('平年');
        }
</script>

<script>
        let grade = prompt('请输入您的成绩:');
        if(grade >= 90){
            alert('优秀');
        }else if(grade >= 70){
            alert('良好');
        }else if(grade >= 60){
            alert('及格');
        }else{
            alert('不及格');
        }
</script>

<script>
        let num1 = prompt('请输入第一个数');
        let num2 = prompt('请输入第二个数');
        console.log(num1 > num2 ? num1 : num2);
</script>

<script>
        let num1 = parseFloat(prompt('请输入第一个数'));
        let num2 = parseFloat(prompt('请输入第二个数'));
        let option = prompt('请输入操作符')
        let result;
        switch(option){
            case '+':
                result = num1 + num2;
                break;
            case '-':
                result = num1 - num2;
                break;
            case '*':
                result = num1 * num2;
                break;
            case '/':
                result = num1 / num2;
                break;
            default:
                alert('请在 + - * / 中选择操作符:');
                break;
        }
        alert('运算的结果为: ' + result);
</script>

<script>
        let i = 0;
        while(i < 10){
            document.write('月薪过万' + `<br />`);
            i++;           
        }
</script>

<script>
        while(prompt('你爱我吗') !== '爱'){}
</script>

    <script>
        let money = 100;
        while(true){
            let op = prompt(`
            请输入您选择的功能:
                1.存钱
                2.取钱
                3.查看余额
                4.退出系统
            `);

            if(op === '4'){
                break;
            }

            switch(op){
                case '1':
                    m = Number(prompt('请输入您要存入的额度:'));
                    money += m;
                    break;
                case '2': 
                    m = Number(prompt('请输入您要取出的额度:'));
                    money -= m;
                    break;
                case '3':
                    alert('您当前的余额为:' + money);
                    break;
                default:
                    alert('请重新选择操作');
                    break;
            }
        }       
</script>

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