Ajax请求与FormData - JavaScript学习

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1、Ajax请求

1.1、GET请求

代码示例

前端代码

<!DOCTYPE html>
<html lang="en">
    <head>
        <title></title>
        <meta charset="UTF-8">
        <meta name="viewport" content="width=device-width, initial-scale=1">
    </head>
    <body>
        <script>
            //创建ajax对象
            var xhr = new XMLHttpRequest();
            //监听请求
            xhr.onreadystatechange = function(){
                if(xhr.readyState === 4 && xhr.status === 200){
                    console.log(xhr.responseText);
                }
            };
            xhr.open("GET","get.php",true);            
            xhr.send(null);
        </script>
    </body>
</html>

后端数据

<?php
  $user['name'] = "zcx";
  $user['pwd'] = "123456";
  echo json_encode($user);
?>

1.2、POST请求

`application/x-www-form-urlencoded`方法代码示例

前端代码

<!DOCTYPE html>
<html lang="en">
    <head>
        <title></title>
        <meta charset="UTF-8">
        <meta name="viewport" content="width=device-width, initial-scale=1">
    </head>
    <body>
        <script>
            //创建ajax对象
            var xhr = new XMLHttpRequest();
            //监听请求
            xhr.onreadystatechange = function(){
                if(xhr.readyState === 4 && xhr.status === 200){
                    console.log(xhr.responseText);
                }
            };         
             xhr.open("POST","post.php",true);
             xhr.setRequestHeader('Content-type','application/x-www-form-urlencoded');
            var user={
                name:"zcx",
                pwd:"123456",
            };
            var data = JSON.stringify(user);
            xhr.send(data);
        </script>
    </body>
</html>

后端代码

<?php
$user = key($_POST);
echo $user;
$data = json_decode($user);
print_r($data);
$data = json_decode($user,true);
print_r($data);
?>

`application/x-www-form-urlencoded`方法代码示例

前端代码

<!DOCTYPE html>
<html lang="en">
    <head>
        <title></title>
        <meta charset="UTF-8">
        <meta name="viewport" content="width=device-width, initial-scale=1">
    </head>
    <body>
        <script>
            //创建ajax对象
            var xhr = new XMLHttpRequest();
            //监听请求
            xhr.onreadystatechange = function(){
                if(xhr.readyState === 4 && xhr.status === 200){
                    console.log(xhr.responseText);
                }
            };          
             xhr.open("POST","post1.php",true);
             xhr.setRequestHeader('Content-type','application/json;charset=utf-8');
            var user={
                name:"zcx",
                pwd:"123456",
            };
             var data = JSON.stringify(user);
            xhr.send(data);
        </script>
    </body>
</html>

后端代码

<?php
$user = file_get_contents('php://input');
echo $user;
$data = json_decode($user);
print_r($data);
$data = json_decode($user,true);
print_r($data);

1.3、FormData

代码示例

前端代码

<!DOCTYPE html>
<html lang="en">
    <head>
        <title></title>
        <meta charset="UTF-8">
        <meta name="viewport" content="width=device-width, initial-scale=1">
        <link href="" rel="stylesheet">
    </head>
    <body>
        <script>
            //创建ajax对象
            var xhr = new XMLHttpRequest();
            //监听请求
            xhr.onreadystatechange = function(){
                if(xhr.readyState === 4 && xhr.status === 200){
                    console.log(xhr.responseText);
                }
            };          
            xhr.open("POST","post2.php",true);
            var data = new FormData();
            data.append("name",'zcx')
            data.append("pwd",'123456')
            xhr.send(data);
        </script>
    </body>
</html>

后端代码

<?php
$user['name'] = $_POST['name'];
$user['pwd'] = $_POST['pwd'];
print_r($user);

2、FormData完成用户登录与验证

代码示例

前端代码

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=<device-width>, initial-scale=1.0">
    <title>Document</title>
    <style>
        body{
            box-sizing: border-box;
            margin: 0px;
            padding: 0px;
        }
        form{
            width: 260px;
            margin: auto;
            margin-top: 50px;
            background-color: #a7c4e0;
            padding: 30px  30px;
            display: grid;  
            gap: 20px;         
        }
    </style>
</head>
<body>
    <form action="" method="POST" onsubmit="return false">
            <div>
                <label>用户名：</label>
                <input type="text" name="name" placeholder="请输入用户名" autofocus required >
            </div>
            <div>
                <label>密    码：</label>
                <input type="password" name="pwd" placeholder="请输入用户名"  required>
            </div>
            <div style="margin:auto;">
                <button>登  录</button>
            </div>            
    </form>
</body>
</html>
<script>
    var form = document.querySelector("form");
    var btn = document.querySelector("form button");
    btn.onclick = function(){
        //创建ajax对象
        var xhr = new XMLHttpRequest();
        //监听请求
        xhr.onreadystatechange = function(){
            if(xhr.readyState === 4 && xhr.status === 200){
                var res = JSON.parse(xhr.responseText);
                switch(res.status){
                    case 0:
                            error = res.message;
                            break;
                    case 1:
                            error = res.message;
                            break;
                    default:
                            error="未知错误";
            }          
                var span = document.createElement("span");
                span.innerHTML = error;
                span.style.color ="red";
                form.appendChild(span);
            }
        };         
        xhr.open("POST","index.php",true);
        var data = new FormData(form);
        xhr.send(data);
    };
    var inputs = document.querySelectorAll("input");
     for(var i = 0;i < inputs.length; i++){
         inputs[i].oninput = function(){
             if(btn.nextElementSibling !== null)  form.removeChild(btn.nextElementSibling)             
         };
     }
</script>

后端代码

<?php
$pdo = new PDO("mysql:host=localhost;dbname=xxyl","root","root");
$sql = "select count(`id`) from `users` where `name`=? and `pwd`=? limit 1";
$stmt = $pdo->prepare($sql);
$stmt->execute([$_POST['name'],md5($_POST['pwd'])]);
$res = $stmt->fetch(PDO::FETCH_NUM);
if($res[0]== 1){
     echo json_encode(['status'=>0,'message'=>'验证成功']);
}else{
    echo json_encode(['status'=>1,'message'=>'用户名或密码错误']);
}