1.json

        let str = '{"name":"张三","age":20,"height":"178cm"}';
        let str2 = '[{"name":"张三","age":20,"height":"178cm"},{"name":"李四","age":21,"height":"179cm"}]';
        console.log(str);
        console.log(str2);
        let obj = {
            name:"李四",
            age:20,
            height:"180cm"
        }
        console.log(obj);

        // 1.数组或者对象转成json字符串 JSON.stringify
        let arr = [
            {name:"zhangsan",age:20},
            {name:"zhangsan2",age:21},
            {name:"zhangsan3",age:22},
        ]

        let josnstr = JSON.stringify(arr);
        console.log(josnstr); //[{"name":"zhangsan","age":20},{"name":"zhangsan2","age":21},{"name":"zhangsan3","age":22}]

        // 2.json字符串转成对象或者数组

        let str = '{"name":"张三","age":20,"height":"178cm"}';
        let str2 = '[{"name":"张三","age":20,"height":"178cm"},{"name":"李四","age":21,"height":"179cm"}]';
         let arr = [
            {name:"zhangsan",age:20},
            {name:"zhangsan2",age:21},
            {name:"zhangsan3",age:22},
        ]
        var arr01 = JSON.parse(str);
		var arr02 = JSON.parse(str2);
		console.log(arr01); //{name: '张三', age: 20, height: '178cm'}
		console.log(arr02);
        var arr2 =   JSON.parse(JSON.stringify(arr));
        console.log(arr2);

        let obj = {name:"1111",age:20,fn(){console.log(111)},c:undefined};
        let obj2 = JSON.parse(JSON.stringify(obj));
        obj2.age = 30;
        console.log(obj2);
        // console.log(obj);

2.全局变量 

//1.$_SERVER
echo "<pre>";
print_r($_SERVER);  // 和服务器相关的一些信息；
echo "</pre>";

print_r($_POST);

print_r($_REQUEST);
//request  :请求  response：返还

// 获取服务器的时间戳 ；2022-1-12  2022/1/12  。。。。----》时间戳 
$time = time();  //获取当前服务器的时间的时间戳 单位是秒 
// echo time();

// 把时间戳转成时间 ；
echo date("Y/m/d H:i:s",$time);

file_put_contents("2.txt",json_encode($_REQUEST));

// php里的跳转:php在返还头部写跳转路径 
// header("Location:post.html");
// 通过js来跳转；
echo "<script>window.location.href='post.html'</script>";

4.数据库操作

// php操作数据库 
// 第一步：通过php连接数据库 
$link =  mysqli_connect("localhost","root","root","2114");
// 第二步：写sql语句；
$sql = "INSERT INTO users(username,age,score) VALUES('李四',23,80)";

// 第三步：通过php执行sql
$res =  mysqli_query($link,$sql);
if($res){
	echo "添加成功";
}else{
	echo "添加失败";
}