ajax在实时搜索中更新之前读取Json文件

Question

我正在使用jquery Ajax编写实时搜索，将关键字发布到php文件，将结果写入JSON文件然后我将此JSON文件作为搜索结果读取。 我的问题是来自JSON的Jquery GET总是检索以前的搜索结果

脚本文件

$("#searchArea").keyup(function() {
var searchKeyword = $(this).val();
        if (searchKeyword.length > 0) {
            $.post('livesearch.php', { keywords: searchKeyword });
            $.getJSON('livesearch.json',function(data){
                var resultBox = $('#searchReasult');
                 var output = '<ul>';
                $.each(data, function(key, val){
                output +=  '<li>';
                output += '<h3>' + val.username + '</h3>';
                output += '</li>';
                })
                output += '</ul>';
                $('#update').html(output);
               console.log(output)
               if(searchKeyword.length=0){$('#update').hide;}
            })
                    }
if(searchKeyword.length=0){$('#update').hide;}

PHP文件

<?php
require_once('includes/database.php');
require_once('includes/USER.php');
$key = (isset($_POST['keywords']))? $_POST['keywords']:null;
if(isset($key)){
    global $database;
    $esc_key = $database->escape_value($key);
    $sql = "SELECT * FROM user ";
    $sql .= "WHERE username LIKE '%$esc_key%' OR ";
    $sql .= " first_name LIKE '%$esc_key%' OR ";
    $sql .= " last_name LIKE '%$esc_key%' ";
    $sql .= "LIMIT 10 ";
    $result = USER::find_by_sql($sql);
    foreach($result as $user){
        $user->password = null;
    }    
    $fp = fopen('livesearch.json', 'w');
    fwrite($fp, json_encode($result));
    fclose($fp);

}?>