使用AJAX发送隐藏的输入数据

I am using AJAX live search plugin.
It passes input data to backend-search.php
backend-search.php selects data from the database and return to the search page.
Now I want to pass one hidden input value with the search query.

Hidden Input

<input type="hidden" name="group" value="<?php echo $grp_id; ?>" />

Following is my html in search.php

<div class="search-box">
   <input type="text" autocomplete="off" placeholder="Search..." />    
<div class="result"></div>

Javascript

<script type="text/javascript">
$(document).ready(function(){
    $('.search-box input[type="text"]').on("keyup input", function(){
        /* Get input value on change */
        var term = $(this).val();
        var resultDropdown = $(this).siblings(".result");
        if(term.length){
            $.get("backend-search.php", {query: term}).done(function(data){
                // Display the returned data in browser
                resultDropdown.html(data);
            });
        } else{
            resultDropdown.empty();
        }
    });
    // Set search input value on click of result item
    $(document).on("click", ".result p", function(){
        $(this).parents(".search-box").find('input[type="text"]').val($(this).text());
        $(this).parent(".result").empty();
    });
});
</script>

How do I send the data of the hidden input field with above js?

</div>

You could use $.post instead of $.get like this:

$.post( "backend-search.php?query="+ term, { hidden_key: "hidden_value"})
.done(function(data) {
    alert( "Data Loaded: " + data );
});

So, customizing it for your code,

if(term.length) {
    // get value of hidden field
    var hidden_value = $('[name="group"]').value(); 
    // make a post request, but also pass query params 
    $.post("backend-search.php?query=" + term, { group: hidden_value})
       .done(function(data){
           // Display the returned data in browser
           resultDropdown.html(data);
        });
    }

Here, everything after the ? mark is passed as a query string (i.e. via get method) whereas the hidden field is passed by the Post method. In your Php script, use print_r($_REQUEST) to verify that you get the 2 parameters as desired.

Also, you should encode URI parameters like this encodeURIComponent(term) to make sure your javascript does not break if the user enters special characters