AJAX and PHP

Chapter 7}{xmlHttp.onreadystatechange = handleGettingResults;xmlHttp.open("GET", url, true);xmlHttp.send(null);}else// if the connection is busy, retry after 1 secondsetTimeout("ajaxRequest(url,callback)", 1000);// called when the state of the request changesfunction handleGettingResults(){// move forward only if the transaction has completedif (xmlHttp.readyState == 4){// a HTTP status of 200 indicates the transaction completed// successfullyif (xmlHttp.status == 200){// execute the callback function, passing the server responseinnerCallback(xmlHttp.responseText)}else{// display error messagealert("Couldn't connect to server");}}}5. The bulk of the client-side work is done by RealTimeChart.js:// SVG namespacevar svgNS = "http://www.w3.org/2000/svg";// the SVG document handlervar documentSVG = null;// will store the root element that groups all chart elementsvar chartGroup = null;// how often to request new data from server?var updateInterval = 1000;// coordinates (in pixels) used to translate the chartvar x = 50, y = 50;// chart's dimension (in pixels)var height = 300, width = 500;// chart's axis originvar xt1 = 0, yt1 = 0;// chart's axis maximum valuesvar xt2 = 50, yt2 = 100;// number of horizontal and vertical axis divisionsvar xDivisions = 10, yDivisions = 10;// default text width and height for initial display (recalculated// afterwards)var defaultTextWidth = 30, defaultTextHeight = 20;// will retain references to the chart units for recalculating positionsvar xIndexes = new Array(xDivisions + 1);var yIndexes = new Array(yDivisions + 1);// will store the text node that displays the selected chart nodevar currentNodeInfo;// retains the latest values generated by servervar lastX = -1, lastY = -1;// shared svg elementsvar chartGroup, dataGroup, dataPath;195