JavaScript基础之对象（附小练习）

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小练习之求100以下的被5整除的数字的和，以及他们的平均值

<!DOCTYPE html><html lang="en"><head>    <meta charset="UTF-8">    <title>作业：求100一下的被5整除的数字的和，及他们的平均值</title></head><body></body><script>    var arr = [];                               //声明空数组，用来装符合条件的数组    for (var i = 1; i < 100; i++) {        if (i % 5 == 0) {            arr.push(i);                         //吧符合条件的数据装入数组        }    }    var sum = 0;    for (var i = 0; i < arr.length; i++) {      //ba数组的所有元素求和        sum += arr[i];    }    alert(sum);    alert(sum / arr.length);</script></html>

排序练习

<!DOCTYPE html><html lang="en"><head>    <meta charset="UTF-8">    <title>排序练习</title></head><body></body><script>    function sortNumber(a,b) {        return b - a;    }    var arr = [3,5,58,34,99,43,77];    var newArr = arr.sort(sortNumber);    document.write(newArr);    var newARR = arr.reverse();    document.write("<br>");    document.write(newARR);</script></html>

传值和传引用

<!DOCTYPE html><html lang="en"><head>    <meta charset="UTF-8">    <title>传值和传引用</title></head><body></body><script>    /*基本数据类型：   传值*/    /*var zhangHeight = 180;     var liHeight = zhangHeight;     zhangHeight = 185;     alert(liHeight);*///    /*引用数据类型：   传引用*///    var zhangSan = [180, 75];//    var liSi = zhangSan;//    zhangSan[0] = 185;//    zhangSan[1] = 80;//    alert(liSi[0]);//    alert(liSi[1]);                           //传值和传引用运行一下就明白了    栈和堆</script></html>

转换成字符串

<!DOCTYPE html><html lang="en"><head>    <meta charset="UTF-8">    <title>转换成字符串</title></head><body></body><script>    //    var num = new Number(5);    //    var num = 5;                            //这两句话意义相同    //    alert(Number.MAX_VALUE);                  //计算机数字中最大值    //    alert(Number.MIN_VALUE);    //    alert(Number.NEGATIVE_INFINITY);          //无穷小    //    alert(Number.POSITIVE_INFINITY);          //无穷大    //    //    //    var i = 5;    //    var j;    //    var result = i +j;    //    alert(result);                              //not a number  NaN    var i = 5;    var result = i.toString();                          //把数字转换成字符串    alert(typeof (result));    var arr = ["zhangsan","lisi"];    var result1 = arr.toString();    console.log(typeof result1);                        //把数组转化成字符串    var b = true;    var result2 = b.toString();                         //把布尔类型的转化成字符串    console.log(result2);</script></html>

字符串

<!DOCTYPE html><html lang="en"><head>    <meta charset="UTF-8">    <title>字符串</title></head><body></body><script>    //    var s = "杰瑞教育";    //    console.log(s.length);                  //把字符串当作是字符数组    //    //    var s1 = "ccy";    //    console.log(s1.toUpperCase());          //把小写转换成大写    //    //    var s2 = "JREDU";    //    console.log(s2.toLowerCase());          //吧大写转换成小写    //    //    var s3 = "jerei";    //    console.log(s3.charAt(2));              //获取字符串中制定索引处的字符    //    //    var s4 = "HelloWorld";    //    //返回字某个字符串第一次出现的索引位置,    //    //参数1：要查找的子元素    //    //参数2：查找的开始位置    //    console.log(s4.indexOf("o",5));    //subString:与数组的slice方法类似，用于截取字符串的某一段子字符    //参数1:截取的开始索引（包含）    //参数2:截取的结束索引（不包含）    var s5 = "this is js";    result = s5.substring(5, 7);    console.log(result);</script></html>

日期属性

<!DOCTYPE html><html lang="en"><head>    <meta charset="UTF-8">    <title>日期</title></head><body><div id="time"></div></body><script>    setInterval(function () {        var date = new Date();        var year = date.getFullYear();                  //获取年        console.log(year);        var month = date.getMonth() + 1;                  //获取月份 +1        console.log(month);        var day = date.getDate();                       //获取日期        console.log(day);        var hour = date.getHours();                     //获取时        console.log(hour);        var min = date.getMinutes();                    //获取分        console.log(min);        var sec = date.getSeconds();                    //获取秒        console.log(sec);        var mSec = date.getMilliseconds();              //获取毫秒        console.log(mSec);        var week = date.getDay() == 0 ? 7 : date.getDay();        console.log(week);        var s = year + "年" + month + "月" + day + "日" + " " + hour + ":" + min + ":" + sec + ":" + mSec + " " + "星期" + week        document.getElementById("time").innerHTML = s;    }, 1000);</script></html>

数学类

<!DOCTYPE html><html lang="en"><head>    <meta charset="UTF-8">    <title>数学类</title></head><body></body><script>    var pi = Math.PI;    console.log(pi);    var r = Math.random();                          //随机生成一个0-1之间的数    console.log(Math.floor(r*11));                  //floor;向下取整    忽略小数取整    var i = -3.5;    console.log(Math.abs(i));                       //取绝对值    console.log(Math.floor(i));                     //floor;向下取整    忽略小数取整    console.log(Math.ceil(i));                      //ceil:向上取整 小数不为0.整数就+1    console.log(Math.round(i));                      //四舍五入取值    var result = Math.max(8,9,23,444,555);          //比较多个数值得最大值    var result2 = Math.min(8,9,23,444,555);          //比较多个数值得最小值    console.log(result);    console.log(result2);    var i2 = 5;    var result3 = Math.pow(i2,3);    console.log(result3);</script></html>

对象！！！

<!DOCTYPE html><html lang="en"><head>    <meta charset="UTF-8">    <title>对象</title></head><body></body><script>    var zhangSan = new Object();    zhangSan.name = "zhangsan";    zhangSan.age = "25";    zhangSan.height = "160";    zhangSan.eat = function () {        alert("wohuichi!");    };    var zhangSan = {        name: "zhangSan",        age: "25",        height: "160",        eat: function () {            alert("wohuichi!");        }    };                                              //于上方一样    delete zhangSan.name;                           //删除对象属性    showMessage(zhangSan);    function showMessage(person) {        console.log(person.name);        console.log(person.age);        console.log(person.height);    }</script></html>

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