Took a little while, but I finally figured out how to add WordPress Media Library multiple image selection for a process partly depicted above, part of a plug-in still in development.
My code follows. As I mentioned at StackExchange WordPress Development – where I first put the issue in the form of a question, at a point when I was unsure of my ability to answer it – I’d be happy to accept and credit improvements on this work from some true jQuery/WordPress expert, though the code seems to be working quite well so far.
/**
* @Script: WordPress Multiple Image Selection in jQuery
* @Version: 0.1
* @Author: CK MacLeod
* @Author URI: https://ckmacleod.com
* @License: GPL3
*/
jQuery(document).ready( function( $ ) {
var myplugin_media_upload;
$('#myplugin-change-image').click(function(e) {
e.preventDefault();
// If the uploader object has already been created, reopen the dialog
if( myplugin_media_upload ) {
myplugin_media_upload.open();
return;
}
// Extend the wp.media object
myplugin_media_upload = wp.media.frames.file_frame = wp.media({
//button_text set by wp_localize_script()
title: button_text.title,
button: { text: button_text.button },
multiple: true //allowing for multiple image selection
});
/**
*THE KEY BUSINESS
*When multiple images are selected, get the multiple attachment objects
*and convert them into a usable array of attachments
*/
myplugin_media_upload.on( 'select', function(){
var attachments = myplugin_media_upload.state().get('selection').map(
function( attachment ) {
attachment.toJSON();
return attachment;
});
//loop through the array and do things with each attachment
var i;
for (i = 0; i < attachments.length; ++i) {
//sample function 1: add image preview
$('#myplugin-placeholder').after(
'<div class="myplugin-image-preview"><img src="' +
attachments[i].attributes.url + '" ></div>'
);
//sample function 2: add hidden input for each image
$('#myplugin-placeholder').after(
'<input id="myplugin-image-input' +
attachments[i].id '" type="hidden"
name="myplugin_attachment_id_array[]" value="' +
attachments[i].id + '">'
);
}
});
myplugin_media_upload.open();
});
});