WordPressで利用しているTinyMCEをテキストの長さに応じて自動で広げる

2014/10/16：追記
WordPress4.0からはデフォルトで、テキストの長さに応じてエディタが広まるようになったようですね。

WordPressのビジュアルエディタでコードを貼り付けたときや長文を書く場合など、いちいちフォームの長さを伸ばすのが面倒ですよね。
TinyMCEのカスタマイズを行うことでテキストの長さに応じて、自動でリサイズすることができるようです。

WordPressのPluginフォルダに「tinymce-autoresize」というディレクトリを作成します。
下記の内容で「tinymce_autoresize.php」という名前のファイルを作成し、先ほどの「tinymce-autoresize」ディレクトリに保存します。

下記の内容で「editor_plugin.js」という名前のファイルを作成し、先ほどの「tinymce-autoresize」ディレクトリに保存します。

/**
 * editor_plugin_src.js
 *
 * Copyright 2009, Moxiecode Systems AB
 * Released under LGPL License.
 *
 * License: http://tinymce.moxiecode.com/license
 * Contributing: http://tinymce.moxiecode.com/contributing
 */

(function() {
    /**
     * Auto Resize
     *
     * This plugin automatically resizes the content area to fit its content height.
     * It will retain a minimum height, which is the height of the content area when
     * it's initialized.
     */
    tinymce.create('tinymce.plugins.AutoResizePlugin', {
        /**
         * Initializes the plugin, this will be executed after the plugin has been created.
         * This call is done before the editor instance has finished it's initialization so use the onInit event
         * of the editor instance to intercept that event.
         *
         * @param {tinymce.Editor} ed Editor instance that the plugin is initialized in.
         * @param {string} url Absolute URL to where the plugin is located.
         */
        init : function(ed, url) {
            var t = this, oldSize = 0;

            if (ed.getParam('fullscreen_is_enabled'))
                return;

            /**
             * This method gets executed each time the editor needs to resize.
             */
            function resize() {
                var deltaSize, d = ed.getDoc(), body = d.body, de = d.documentElement, DOM = tinymce.DOM, resizeHeight = t.autoresize_min_height, myHeight;

                // Get height differently depending on the browser used
                myHeight = tinymce.isIE ? body.scrollHeight : (tinymce.isWebKit && body.clientHeight == 0 ? 0 : body.offsetHeight);

                // Don't make it smaller than the minimum height
                if (myHeight > t.autoresize_min_height)
                    resizeHeight = myHeight;

                // If a maximum height has been defined don't exceed this height
                if (t.autoresize_max_height && myHeight > t.autoresize_max_height) {
                    resizeHeight = t.autoresize_max_height;
                    body.style.overflowY = "auto";
                    de.style.overflowY = "auto"; // Old IE
                } else {
                    body.style.overflowY = "hidden";
                    de.style.overflowY = "hidden"; // Old IE
                    body.scrollTop = 0;
                }

                // Resize content element
                if (resizeHeight !== oldSize) {
                    deltaSize = resizeHeight - oldSize;
                    DOM.setStyle(DOM.get(ed.id + '_ifr'), 'height', resizeHeight + 'px');
                    oldSize = resizeHeight;

                    // WebKit doesn't decrease the size of the body element until the iframe gets resized
                    // So we need to continue to resize the iframe down until the size gets fixed
                    if (tinymce.isWebKit && deltaSize < 0)
                        resize();
                }
            };

            t.editor = ed;

            // Define minimum height
            t.autoresize_min_height = parseInt(ed.getParam('autoresize_min_height', ed.getElement().offsetHeight));

            // Define maximum height
            t.autoresize_max_height = parseInt(ed.getParam('autoresize_max_height', 0));

            // Add padding at the bottom for better UX
            ed.onInit.add(function(ed){
                ed.dom.setStyle(ed.getBody(), 'paddingBottom', ed.getParam('autoresize_bottom_margin', 25) + 'px');
            });

            // Add appropriate listeners for resizing content area
            ed.onChange.add(resize);
            ed.onSetContent.add(resize);
            ed.onPaste.add(resize);
            ed.onKeyUp.add(resize);
            ed.onPostRender.add(resize);

            if (ed.getParam('autoresize_on_init', true)) {
            //  ed.onLoad.add(resize);
                ed.onLoadContent.add(resize);
            }

            // Register the command so that it can be invoked by using tinyMCE.activeEditor.execCommand('mceExample');
            ed.addCommand('mceAutoResize', resize);
        },

        /**
         * Returns information about the plugin as a name/value array.
         * The current keys are longname, author, authorurl, infourl and version.
         *
         * @return {Object} Name/value array containing information about the plugin.
         */
        getInfo : function() {
            return {
                longname : 'Auto Resize',
                author : 'Moxiecode Systems AB',
                authorurl : 'http://tinymce.moxiecode.com',
                infourl : 'http://wiki.moxiecode.com/index.php/TinyMCE:Plugins/autoresize',
                version : tinymce.majorVersion + "." + tinymce.minorVersion
            };
        }
    });
    // Register plugin
    tinymce.PluginManager.add('autoresize', tinymce.plugins.AutoResizePlugin);
})();