How are Javascript-js and PHP related to each other?

JS section:
$ ('. New-title-info-btn '). MouseEnter (

    function(){        var key=$(this).attr('class').split(" ")[1];//这里key取单独给他们的class值        $('.'+key).click(function(){            $.ajax({                 url:"js4-1.php?type=findnew",                 data:key,           //我想把变量key的值当数据发送给php,这里不知道怎么写才能把变量key的值发给php                success:function(key){                 //这里我想获取到php回调的两个数据(new_title,new_class的值),然后反馈给前段修改主页面内容?                    console.log(key);                },                 error:function(e){                     console.error(e);                 }             });        //console.log(key);        })    })

Php:
$type =@$_get[' type '];
$sleword =@$_get[' data '];//here to get JS sent over
Switch ($type) {

case findnew:    $sql="select new_title,new_class from info_look";//这里的语句,我想把变量$sleword当作条件加到where后面即select new_title,new_class from info_look where new_calss=$sleword这样子,具体要怎么写才能在sql语句里应用变量sleword?    $keyword=mysql_query($sql);//执行语句    $wordArray=[];//创建空字符串承载获取到的数据    while($row=mysql_fetch_array($keyword)){        //$wordArray=$row;        //这里能不能return回调$sql查询到的new_title,new_class给js,然后让js插入到指定的页面标签中去?    }    //print_r($wordArray);    break;

}

The questions are written in the comments, the new problem, so there is a wrong place to say thank you for pointing out, if you can, I hope you help me to see how I want to write this method, thank you

Reply content:

JS section:
$ ('. New-title-info-btn '). MouseEnter (

    function(){        var key=$(this).attr('class').split(" ")[1];//这里key取单独给他们的class值        $('.'+key).click(function(){            $.ajax({                 url:"js4-1.php?type=findnew",                 data:key,           //我想把变量key的值当数据发送给php,这里不知道怎么写才能把变量key的值发给php                success:function(key){                 //这里我想获取到php回调的两个数据(new_title,new_class的值),然后反馈给前段修改主页面内容?                    console.log(key);                },                 error:function(e){                     console.error(e);                 }             });        //console.log(key);        })    })

Php:
$type =@$_get[' type '];
$sleword =@$_get[' data '];//here to get JS sent over
Switch ($type) {

case findnew:    $sql="select new_title,new_class from info_look";//这里的语句,我想把变量$sleword当作条件加到where后面即select new_title,new_class from info_look where new_calss=$sleword这样子,具体要怎么写才能在sql语句里应用变量sleword?    $keyword=mysql_query($sql);//执行语句    $wordArray=[];//创建空字符串承载获取到的数据    while($row=mysql_fetch_array($keyword)){        //$wordArray=$row;        //这里能不能return回调$sql查询到的new_title,new_class给js,然后让js插入到指定的页面标签中去?    }    //print_r($wordArray);    break;

}

The questions are written in the comments, the new problem, so there is a wrong place to say thank you for pointing out, if you can, I hope you help me to see how I want to write this method, thank you

$.ajaxparameter to add a field dataType: 'json' , and then in PHP to the data you want to pass to JS to use a function to make a json_encode JSON string echo or die go out on the line.

