JavaScript内置对象
JavaScript中的对象分为3种：内置对象/浏览器对象/自定义对象
JavaScript内置对象
Array数组类型
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<script>
var a1 = new Array(); //定义一个空数组
var a2 = new Array(10); //定义一个长度为10数组（值：undefined）
var a3 = new Array(10,20,30); //定义一个指定数值的数组
console.log(a1.length);//0
console.log(a2.length);//10
console.log(a3.length);//3
var a4 = [10,20,30,40,50];//快捷定义数组
//数组遍历
for(var i=0; i<a4.length; i++){
console.log(i,"=>",a4[i]);
}
//for in 遍历数组
for(var i in a4){
console.log(i,"=>",a4[i]);
}
//forEach 遍历数组
a4.forEach(function(v){
console.log(v);
});
//数组的方法:
console.log(a4.toString());
console.log(a4.join(":"));
var aa = new Array(10,20,30);
console.log(aa.join(":"));
aa.push(50);
aa.push(40);
console.log(aa.join(":"));
</script>
</head>
<body>
</body>
</html>
基本包装类型
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<script>
//内置对象--基本包装类型
var s1 = 'zhangsan';
console.log(s1.substring(2,5))
//等价于
var s2 = new String("zhangsan");
console.log(s2.substring(2,5));
var num = 20.5678;
console.log(num.toFixed(2));//保留小数点后两位 四舍五入
</script>
</head>
<body>
</body>
</html>
Date日期
var dd = new Date();
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=, initial-scale=1.0">
<title>Document</title>
</head>
<script>
//内置对象 --date日期对象
var dd = new Date();
//从1970年1月1日0时0分0秒至今的毫秒数
document.write("时间戳"+dd.valueOf);
function formatDate(d){
if(!d instanceof Date){
return;
}
var y = d.getFullYear(),
m = d.getMonth()+1,
day = d.getDate(),
hh = d.getHours(),
mm = d.getMinutes(),
ss = d.getSeconds();
//判断单位数字前补零操作
hh = hh<10?'0'+hh:hh;
mm = mm<10?'0'+mm:mm;
ss = ss<10?'0'+ss:ss;
return y+"-"+m+"-"+day+" "+hh+":"+mm+":"+ss;
}
//内置对象 --date日期对象
var dd = new Date();
//从1970年1月1日0时0分0秒至今的毫秒数
document.write("时间戳"+dd.valueOf);
document.write("<h2>"+formatDate(dd)+"</h2>");
</script>
<body>
</body>
</html>
String字符串
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
</head>
<body>
</body>
<script>
//内置对象--String字符串对象
var s1 = "zhangsanfeng";
document.write(s1+"<br/>");
document.write(s1[5]+"<br/>");
document.write(s1.substr(5,3)+"<br/>");
document.write(s1.substring(5,8)+"<br/>");
document.write("小写："+s1.toLowerCase()+"<br/>");
document.write("大写："+s1.toUpperCase()+"<br/>");
//子串查找
document.write(s1.indexOf("an")+"<br/>");
document.write(s1.lastIndexOf("an")+"<br/>");
//替换
document.write(s1.replace("sanfeng","wuji")+"<br/>");
//全部替换
document.write("10,20,30,40".replace(/,/g,"：")+"<br/>");
var str = "10:23:45:67:87";
console.log(str);
console.log(str.split(":"));
var s2 = " zhangsan ";
//去除两边多余字符
console.log("#"+s2+"#");
console.log("#"+ s2.trim()+"#");
</script>
</html>
Math对象
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
</head>
<body>
</body>
<script>
//内置对象--Math对象
console.log(Math.abs(-20));//绝对值
console.log(Math.ceil(10.0000001));//进一取整
console.log(Math.floor(10.999999));//舍去取整
console.log(Math.round(10.5));//四舍五入取整
console.log(Math.max(10,20));//取大
console.log(Math.min(10,20));//取小
console .log(Math.random());//0~1的随机数
console .log(Math.ceil(Math.random()*1000000)%10+1);//1~10的随机数
</script>
</html>
