[GitHub] wicket pull request #258: Wicket 6498 deferred javascript made simple

[martin-g <gi...@git.apache.org>]

Github user martin-g commented on a diff in the pull request:

    https://github.com/apache/wicket/pull/258#discussion_r165631611
  
    --- Diff: wicket-core/src/main/java/org/apache/wicket/markup/head/filter/JavaScriptDeferHeaderResponse.java ---
    @@ -0,0 +1,141 @@
    +/*
    + * Licensed to the Apache Software Foundation (ASF) under one or more
    + * contributor license agreements.  See the NOTICE file distributed with
    + * this work for additional information regarding copyright ownership.
    + * The ASF licenses this file to You under the Apache License, Version 2.0
    + * (the "License"); you may not use this file except in compliance with
    + * the License.  You may obtain a copy of the License at
    + *
    + *      http://www.apache.org/licenses/LICENSE-2.0
    + *
    + * Unless required by applicable law or agreed to in writing, software
    + * distributed under the License is distributed on an "AS IS" BASIS,
    + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    + * See the License for the specific language governing permissions and
    + * limitations under the License.
    + */
    +package org.apache.wicket.markup.head.filter;
    +
    +import org.apache.wicket.core.util.string.JavaScriptUtils;
    +import org.apache.wicket.markup.head.AbstractJavaScriptReferenceHeaderItem;
    +import org.apache.wicket.markup.head.HeaderItem;
    +import org.apache.wicket.markup.head.IHeaderResponse;
    +import org.apache.wicket.markup.head.IWrappedHeaderItem;
    +import org.apache.wicket.markup.head.JavaScriptContentHeaderItem;
    +import org.apache.wicket.markup.head.JavaScriptHeaderItem;
    +import org.apache.wicket.markup.head.OnDomReadyHeaderItem;
    +import org.apache.wicket.markup.head.OnLoadHeaderItem;
    +import org.apache.wicket.markup.html.DecoratingHeaderResponse;
    +import org.apache.wicket.page.PartialPageUpdate;
    +import org.apache.wicket.request.Response;
    +import org.apache.wicket.util.string.Strings;
    +
    +/**
    + * A header response that defers all {@link AbstractJavaScriptReferenceHeaderItem}s.
    + * <p>
    + * To prevent any error because of possible dependencies to referenced JavaScript files
    + * *all* {@link JavaScriptHeaderItem}s are replaced with suitable implementations that
    + * delay any execution until {@link AbstractJavaScriptReferenceHeaderItem}s have been loaded.
    + * 
    + * @author svenmeier
    ++ */
    +public class JavaScriptDeferHeaderResponse extends DecoratingHeaderResponse
    +{
    +	/**
    +	 * Decorate the given response.
    +	 * 
    +	 * @param response
    +	 */
    +	public JavaScriptDeferHeaderResponse(IHeaderResponse response)
    +	{
    +		super(response);
    +	}
    +	
    +	@Override
    +	public void render(HeaderItem item)
    +	{
    +		if (item instanceof IWrappedHeaderItem) {
    +			item = ((IWrappedHeaderItem)item).getWrapped();
    +		}
    +
    +		if (item instanceof AbstractJavaScriptReferenceHeaderItem) {
    +			((AbstractJavaScriptReferenceHeaderItem)item).setDefer(true);
    +		} else if (item instanceof JavaScriptContentHeaderItem) {
    +			item = new NativeOnDomContentLoadedHeaderItem(((JavaScriptContentHeaderItem)item).getJavaScript());
    +		} else if (item instanceof OnDomReadyHeaderItem) {
    +			item = new NativeOnDomContentLoadedHeaderItem(((OnDomReadyHeaderItem)item).getJavaScript());
    +		} else if (item instanceof OnLoadHeaderItem) {
    +			item = new NativeOnLoadHeaderItem(((OnLoadHeaderItem)item).getJavaScript());
    +		}
    +		
    +		super.render(item);
    +	}
    +
    +	/**
    +	 * A specialization that uses native "DOMContentLoaded" events without dependency to external JavaScript.
    +	 * <p>
    +	 * For Ajax requests we utilize the fact, that {@link PartialPageUpdate} renders {@link #getJavaScript()} only,
    +	 * executing the JavaScript directly without any event registration.
    +	 */
    +	private class NativeOnDomContentLoadedHeaderItem extends OnDomReadyHeaderItem
    +	{
    +		private static final long serialVersionUID = 1L;
    +
    +		/**
    +		 * Construct.
    +		 *
    +		 * @param javaScript
    +		 */
    +		public NativeOnDomContentLoadedHeaderItem(CharSequence javaScript)
    +		{
    +			super(javaScript);
    +		}
    +
    +		/**
    +		 * Overriden to use native {@code addEventListener('DOMContentLoaded')} instead.
    +		 */
    +		@Override
    +		public void render(Response response)
    +		{
    +			CharSequence js = getJavaScript();
    +			if (Strings.isEmpty(js) == false)
    +			{
    +				JavaScriptUtils.writeJavaScript(response, "document.addEventListener('DOMContentLoaded', function() { " + js + "; });");
    +			}
    +		}
    +	}
    +	
    +	/**
    +	 * A specialization that uses native "load" events without dependency to external JavaScript 
    +	 * <p>
    +	 * For Ajax requests we utilize the fact, that {@link PartialPageUpdate} renders {@link #getJavaScript()} only,
    +	 * executing the JavaScript directly without any event registration.
    +	 */
    +	private class NativeOnLoadHeaderItem extends OnLoadHeaderItem
    --- End diff --
    
    `static` ?!


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