Js入门基础知识练习

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    <title>javascript基础练习</title>
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        document.write("换行的使用 <br/>，已经完成换行！");
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    <script src="text.js">外部引用的写法</script>
    <input type="button" value="点击这里" onclick='alert("成功点击");'>

    <br><br>
    <p>JS的五种数据类型：undefined, number, string, boolean, object, function.</p>

    <br><br>
    <p style="color: red; font-size: 40px;">局部变量和全局变量</p>
    <script type="text/javascript">
        var a = 12;
        function fun() {
            var a = 23;
            document.writeln(a);
        }
        document.writeln("fun()");
        fun();
        document.writeln(a);
        var c = (a>=12)?15:0; 
        document.writeln(c);
        console.log(typeof a);
    </script>

    <br><br>
    <p>JS中算术运算符：+,-,*,/,%,++,--,-</p>
    <p>比较运算符： >, <, >=, <=, ==, ===, !=, !==</p>
    <p>逻辑运算符： !, &&, ||</p>


    <br><br>
    <P style="color: red; font-size: 40px;">写99乘法表</P>
    <p style="text-align: left;">
        <script type="text/javascript">
            //var i = 1, j = 1;
            for (var i = 1; i <= 9; i++) {
                for (var j = 1; j <= i; j++)
                {
                    document.writeln(i + '*' + j + '=' + (i*j) +' ');
                }
                document.writeln('<br/>')
            }
        </script>
    </p>


    <br><br>
    <p style="color: red; font-size: 40px;">字符串转化为数字</p>
    <script type="text/javascript">
        var a = "657xxx";
        var b = "78.89xxx";
        var c = 123;
        document.writeln('a' + '= ' + a + '<br/>');
        document.writeln('b' + '= ' + b + '<br/>');
        document.writeln('c' + '= ' + c + '<br/>');
        document.writeln("parseInt(a)" + "=" + parseInt(a) + "<br/>");
        document.writeln("parseInt(b)" + "=" + parseInt(b) + "<br/>");
        document.writeln("parseInt(a)" + "=" + parseFloat(a) + "<br/>");
        document.writeln("parseInt(b)" + "=" + parseFloat(b) + "<br/>");
        document.writeln("isNaN(a)" + "=" + isNaN(a) + "<br/>");
        document.writeln("isNaN(c)" + "=" + isNaN(c) + "<br/>");
    </script>


    <br><br>
    <p style="color: red; font-size: 40px;">Math的使用</p>
    <script type="text/javascript">
        document.writeln("Math.random()" + "产生的随机数：" + Math.random() + "<br/>");
        document.writeln("Math.random()" + "产生的随机数：" + Math.random() + "<br/>");
        document.writeln("Math.max(12,13,-28)" + "最大值结果为：" + Math.max(12,13,-28) + "<br/>");
        document.writeln("Math.pow(2,10)" + "2的10次方：" + Math.pow(2,10) + "<br/>");
    </script>


    <br><br>
    <p style="color: red; font-size: 40px;">字符串的使用</p>
    <script type="text/javascript">
        var str = "Hello,kit,tom,jerry!";
        document.write("str" + "=" + str + "<br/>");
        document.writeln("str.length" + "=" + str.length + "<br>");
        var array = str.split(",");
        for (var i = array.length - 1; i >= 0; i--) {
            document.writeln(array[i] + "<br/>");
        }
        for (var i = str.length; i > 0; i--) {
            document.writeln(str.substring(0,i) + "<br/>");
        }
    </script>




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Js入门基础知识练习

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