birt report qr code I COMMUNICATING WITH THE SERVER: SENDING REQUESTS AND PROCESSING RESPONSES in Font

Generator DataMatrix in Font I COMMUNICATING WITH THE SERVER: SENDING REQUESTS AND PROCESSING RESPONSES

CHAPTER 3 I COMMUNICATING WITH THE SERVER: SENDING REQUESTS AND PROCESSING RESPONSES
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Table 3-3. W3C DOM Properties and Methods Useful When Creating Content Dynamically
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Property/Method
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document.createElement(tagName)
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The createElement method on the document object creates the element specified by tagName. Providing the string div as the method parameter produces a div element. This document object s createTextNode method creates a node containing static text. The appendChild method adds the specified node to the current element s list of child nodes. For example, you can add an option element as a child node of a select element. These methods, respectively, get and set the value of the attribute name of the element. This inserts the node newNode before the element targetNode as a child of the current element. This removes the attribute name from the element. This removes the element childNode from the element. This method replaces the node oldNode with the node newNode. This method returns a Boolean indicating whether the element has any child elements.
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document.createTextNode(text) <element>.appendChild(childNode)
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<element>.getAttribute(name) <element>.setAttribute(name, value) <element>.insertBefore(newNode, targetNode) <element>.removeAttribute(name) <element>.removeChild(childNode) <element>.replaceChild(newNode, oldNode) <element>.hasChildnodes()
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A WORD ABOUT BROWSER INCOMPATIBILITIES
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Despite the continually improving implementation of the W3C DOM and JavaScript in modern Web browsers, some quirks and incompatibilities still cause headaches when developing with the DOM and JavaScript. Internet Explorer has the most limited implementation of the W3C DOM and JavaScript. In the early 2000s, Internet Explorer by some accounts held more than 95 percent of the total browser market, and with no competition in sight, Microsoft chose not to completely implement the various Web standards. You can work around most of these quirks, although doing so makes the scripting messier and nonstandard. For example, a <tr> element added directly to a <table> using appendChild will not appear in Internet Explorer, but it does in other browsers. The workaround is to add the <tr> element to the table s <tbody> element. This workaround performs correctly in all browsers. Internet Explorer also has trouble with the setAttribute method. Internet Explorer won t correctly set the class attribute using setAttribute. The cross-browser workaround is to use both setAttribute("class", "newClassName") and setAttribute("className", "newClassName"). Also, you cannot set the style attribute using setAttribute in Internet Explorer. Instead of using <element>.setAttribute("style, "font-weight:bold;"), the most browsercompatible technique is <element>.style.cssText = "font-weight:bold;";. The examples in this book will adhere as closely as possible to the W3C DOM and JavaScript standards but will stray from the standards when necessary to ensure compatibility with most modern browsers.
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CHAPTER 3 I COMMUNICATING WITH THE SERVER: SENDING REQUESTS AND PROCESSING RESPONSES
The following example demonstrates how you can use the W3C DOM and JavaScript to dynamically create content. The example is a fictional search engine for real estate listings. Clicking the Search button on the form will retrieve the results in XML format using the XMLHttpRequest object. The response XML will be processed using JavaScript to produce a table that lists the results of the search (see Figure 3-3).
Figure 3-3. The results of the search were created dynamically using W3C DOM methods and JavaScript. The XML returned by the server is simple (see Listing 3-5). The root properties node contains all the resulting property elements. Each property element contains three child elements: address, price, and comments. Listing 3-5. dynamicContent.xml < xml version="1.0" encoding="UTF-8" > <properties> <property> <address>812 Gwyn Ave</address> <price>$100,000</price> <comments>Quiet, serene neighborhood</comments> </property> <property> <address>3308 James Ave S</address> <price>$110,000</price> <comments>Close to schools, shopping, entertainment</comments> </property>
CHAPTER 3 I COMMUNICATING WITH THE SERVER: SENDING REQUESTS AND PROCESSING RESPONSES
<property> <address>98320 County Rd 113</address> <price>$115,000</price> <comments>Small acreage outside of town</comments> </property> </properties> The JavaScript for actually sending the request to the server and responding to its response is the same as previous examples. The differences begin in the handleReadyStateChange function. Assuming the request completes successfully, the first thing that happens is that the content created by any previous searches is deleted by calling the clearPreviousResults function. The clearPreviousResults function performs two tasks: removing the Results header text that appears at the top and clearing any rows from the results table. The header text is removed by first checking to see whether the span that surrounds the header text has any children by using the hasChildNodes method. You know that the header text exists if the hasChildNodes method returns true; if it does, delete the first (and only) child node of the span element, as that child node represents the header text. The next task in clearPreviousResults is to delete any rows that may already be in the table displaying the search results. Any result rows are child nodes of the tbody node, so you start by obtaining a reference to that node using the document.getElementById method. Once you have the tbody node, you iterate for as long as the tbody node has child nodes, where the child nodes are tr elements. During each iteration the first child node in the childNodes collection is removed from the table body. The iteration ends once no more rows are left in the table body. The table of search results is built in the parseResults function. This function starts by creating a local variable named results, which is the XML document retrieved from the XMLHttpRequest object s responseXML property. You use the getElementsByTagName method to retrieve all the property elements in the XML document as an array and assign the array to the local variable properties. Once you have the array of property elements, you can iterate over each element in the array and retrieve the property s address, price, and comments. var properties = results.getElementsByTagName("property"); for(var i = 0; i < properties.length; i++) { property = properties[i]; address = property.getElementsByTagName("address")[0].firstChild.nodeValue; price = property.getElementsByTagName("price")[0].firstChild.nodeValue; comments = property.getElementsByTagName("comments")[0].firstChild.nodeValue; addTableRow(address, price, comments); } Let s examine this iteration closely, as this is the heart of the parseResults function. Within the for loop the first thing that happens is you get the next element in the array and assign it to the local property named property. Then, for each of the child elements in which you re interested address, price, and comments you retrieve their respective node values.
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