xmlhttp.readyState 返回 2 即使 xmlhttp.status 等于 200答案

【问题标题】：xmlhttp.readyState returns 2 even though xmlhttp.status equals 200xmlhttp.readyState 返回 2 即使 xmlhttp.status 等于 200
【发布时间】：2016-07-02 15:50:15
【问题描述】：

我正在通过 ajax 发送电子邮件以联系 php。 php 脚本成功发送电子邮件，但即使 xmlhttp.status 为 200，ajax xmlhttp.readyState 仍在继续返回 2。

params = "name=" + name + "&email=" + email + "&message=" + message + "&telephone=" + telephone;

xmlhttp.open("POST", "contact.php", true);
xmlhttp.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
xmlhttp.setRequestHeader("Content-length", params.length);
xmlhttp.setRequestHeader("Connection", "close");
xmlhttp.onreadystatechange = function(){
    if(xmlhttp.readyState == 4 && xmlhttp.status == 200){

        if(xmlhttp.responseText == "fill_form"){
            note.innerHTML = "Please fill the required fields properly";
            return;
        }

        if(xmlhttp.responseText == "Sent"){
            serverMessage.innerHTML = "Thanks. If it is a request or complaint we well get back to you soon";
        }
    }
    else{
        serverMessage.innerHTML = "Some internal error occured while sending the email. Please try again later";
        $('#myModal').modal('show')
    }

    submitBtn.innerHTML = "SEND MESSAGE";
    submitBtn.disabled = false;
}

联系方式.php

<?php

$name=$_POST['name'];
$email=$_POST['email'];
$message=$_POST['message'];
$telephone=$_POST['telephone'];

$mail_to_send_to = "abc@gmail.com";
$feed_back_mail = "name@myDomainName.com";

if (empty($name) || empty($email)|| empty($message))
{
    echo "fill_form";
}
else{

    $from="From:$feed_back_mail"."\r\n"."Reply-To:$email"."\r\n" ;
    $subject="Users feed back Contact";

    if(empty($telephone)){
        $telephone = "No telephone sent my user";    
    }

    $message = "Telephone: $telephone\r\nSender's Email : $email \r\n \r\n$message \r\n";

$isSent = mail($mail_to_send_to, $subject, $message, $from);

    if($isSent){
        echo $isSent;
    }
    else{
        echo "not_sent";
    }
}

做错了什么？

【问题讨论】：

标签： javascript php

【解决方案1】：

请记住，您的 onreadystatechange 回调将在就绪状态更改时被多次调用。您当前的代码响应期望它完成的 first 回调。但是，在之前收到readyState2（“收到的标头”）的电话是很正常的。

所以等到你收到readyState 4：

xmlhttp.onreadystatechange = function(){
    if(xmlhttp.readyState == 4){
        // Done, what happened?
        if(xmlhttp.status == 200){
            // All good
        }
        else{
            // Something went wrong
        }
    }
};

【讨论】：

【解决方案2】：

xmlhttp.readyState 持有 XMLHttpRequest 的状态。

可以是0到4：

0: request not initialized 
1: server connection established
2: request received 
3: processing request 
4: request finished and response is ready

xmlhttp.status 表示你刚刚提出的请求的状态码。

更多来自developer.mozilla.org

XMLHttpRequest.readyState 属性返回 XMLHttpRequest 客户端所处的状态。

0   UNSENT              Client has been created. open() not called yet.
1   OPENED              open() has been called.
2   HEADERS_RECEIVED    send() has been called, and headers and status are available.
3   LOADING             Downloading; responseText holds partial data.
4   DONE                The operation is complete.

2 表示 send() 已被调用并已收到响应头。

4 表示 提取操作完成。这可能意味着数据传输已成功完成或失败。

所以你应该一直等待 readyState 4。

https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest/readyState

【讨论】：