loop posts of wordpress into json array

wp-posts.php

<?php //get_header(); ?>
<?php header('Content-type: text/json; charset=utf-8'); ?>

<?php
/*
$jarr=array(
    'total' =>  239,
    'list'  =>  array(
        array(
        'code'=>'001',
        'name'=>'中国',
        'addr'=>'Address 11',
        'col4'=>'col4 data'
        ),
        array(
        'code'=>'002',
        'name'=>'Name 2',
        'addr'=>'Address 12',
        'col4'=>'col4 data'
        ),
    )
);
*/
$jarr=array();
?>

<?php // Loops of WordPress, see https://digwp.com/2011/05/loops/ ?>
<?php 
$showposts = isset($_GET["showposts"]) ? $_GET["showposts"] : 7; // default to fetch seven posts
$custom_query = new WP_Query('cat=4&showposts='.$showposts); // cat=-9 means exclude category 9
while($custom_query->have_posts()) : 
    $custom_query->the_post();
    global $post;
    $jarr[]=array('id'=>$post->ID,'title'=>$post->post_title,'excerpt'=>$post->post_excerpt,'permalink'=>get_permalink($post));
?>

<?php endwhile; ?>
<?php wp_reset_postdata(); // reset the query ?>



<?php
//echo 'Now:       '. date('Y-m-d H:i:s') ."\n";
echo $str=json_encode($jarr);
?>
            
<?php //get_footer(); ?>