《中级前端1.7》JavaScript内置对象——String,Date,Array,Math

JavaScript一切皆对象，所以也存在很多内置的对象，这些内置对象可以帮我们提供很多方便。

 

什么是对象

创建自定义对象：

方法1

<!-- 创建对象 -->
<script>
    people = new Object();
    people.name = "woodk";
    people.age = "26";
    document.write("name:" + people.name + ",age:" + people.age);
</script>

方法2

<!-- 创建对象 -->
<script>
    people = {
        name: "woodk",
        age: "26"
    };
    document.write("name:" + people.name + ",age:" + people.age);
</script>

方法3，使用函数来定义对象

<!-- 使用函数来定义并创建对象 -->
<script>
    function people(name, age) {
        this.name = name;
        this.age = age;
    }
    son = new people("woodk", 26);
    document.write("name:" + son.name + ",age:" + son.age);
</script>

 

JS内置对象-String字符串对象

<script>
    var str = "Hello World";
    document.write("字符串长度为：" + str.length);
    document.write(str.indexOf("World")); //匹配到，返回索引位置；匹配不到，返回-1
    document.write(str.match("World")); //匹配到，返回World；匹配不到，返回null
    document.write(str.replace("World", "girl"));
</script>

字符串转换为数组：

<script>
    //较常用，字符串分割
    var str1 = "hello,jike,xueyuan";
    var s = str1.split(",");
    document.write(s[1]);
</script>

 

JS内置对象-Date日期对象

常用方法：

<script>
    var date = new Date();
    document.write(date); //Wed Jan 13 2016 03:03:17 GMT+0800 (中国标准时间)
    document.write(date.getFullYear()); //获取年份
    document.write(date.getTime()); //获取时间戳
    date.setFullYear(2010, 9, 1);
    document.write(date);
</script>

每秒刷新的时钟：

<div id="timtTxt">s</div>
<script>
    startTime();
    //时钟
    function startTime() {
        var today = new Date();
        var h = today.getHours();
        var m = today.getMinutes();
        var s = today.getSeconds();
        m = checkTime(m);
        s = checkTime(s);
        document.getElementById("timtTxt").innerHTML = h + ":" + m + ":" + s;
        t = setTimeout(function() {
            startTime();
        }, 1000);
    }
    
    //如果分和秒是个位数时，前面加上一个0
    function checkTime(i) {
        if (i < 10) {
            i = "0" + i;
        }
        return i;
    }
</script>

网页显示：

 

JS内置对象-Array数组对象

<!-- 合并数组 -->
<script>
    var a = ["hello", "world"];
    var b = ["woodk", "man"];
    var c = a.concat(b);
    document.write(c);
</script>

<!-- 排序 -->
<script>
    var s1 = ["a", "c", "d", "t", "b", "e"];
    document.write(s1.sort());
    var s2 = [1, 5, 3, 4, 2];
    document.write(s2.sort());
    document.write(s2.sort(function(a, b) {
        return a - b; //升序
    }));
    document.write(s2.sort(function(a, b) {
        return b - a; //降序
    }));
</script>

<!-- 末尾追加元素 -->
<script>
    var arr1 = ["a", "b"];
    arr1.push("ccc");
    document.write(arr1);
</script>

<!-- 数组元素翻转 -->
<script>
    var arr = ["a", "c", "b"];
    document.write(arr.reverse());
</script>

splice()添加，删除数组中元素：

arr.splice(2,0,"William");  //添加
arr.splice(2,1,"William");  //删除并添加
arr.splice(2,3,"William");  //删除3个并添加

 

 

JS内置对象-Math对象

<!-- Math数学对象 -->
<script>
    document.write(Math.round(2.5) + "<br>"); //四舍五入
    document.write(Math.random() + "<br>"); //随机数从0-1
    document.write(parseInt(Math.random() * 10) + "<br>"); //随机一个从0-10的整数
    /*每隔1秒输出一个随机数*/
    showRandom();

    function showRandom() {
        document.write(parseInt(Math.random() * 10) + ","); //随机一个从0-10的整数        
        setTimeout(function() {
            showRandom();
        }, 1000);
    }
    document.write(Math.max(19, 21, 2, 3)); //最大值
    document.write(Math.min(19, 21, 2, 3)); //最小值
    document.write(Math.min.apply(null, [19, 21, 2, 3])); //传递数组，获取最小值
    document.write(Math.abs(-10)); //绝对值
    document.write(Math.floor(5.335)); //输出5； floor获取一个小于或等于目标数字的最接近的整数
</script>