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 second
setTimeout("ajaxRequest(url,callback)", 1000);
// called when the state of the request changes
function handleGettingResults()
{
// move forward only if the transaction has completed
if (xmlHttp.readyState == 4)
{
// a HTTP status of 200 indicates the transaction completed
// successfully
if (xmlHttp.status == 200)
{
// execute the callback function, passing the server response
innerCallback(xmlHttp.responseText)
}
else
{
// display error message
alert("Couldn't connect to server");
}
}
}
5. The bulk of the client-side work is done by RealTimeChart.js:
// SVG namespace
var svgNS = "http://www.w3.org/2000/svg";
// the SVG document handler
var documentSVG = null;
// will store the root element that groups all chart elements
var chartGroup = null;
// how often to request new data from server?
var updateInterval = 1000;
// coordinates (in pixels) used to translate the chart
var x = 50, y = 50;
// chart's dimension (in pixels)
var height = 300, width = 500;
// chart's axis origin
var xt1 = 0, yt1 = 0;
// chart's axis maximum values
var xt2 = 50, yt2 = 100;
// number of horizontal and vertical axis divisions
var 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 positions
var xIndexes = new Array(xDivisions + 1);
var yIndexes = new Array(yDivisions + 1);
// will store the text node that displays the selected chart node
var currentNodeInfo;
// retains the latest values generated by server
var lastX = -1, lastY = -1;
// shared svg elements
var chartGroup, dataGroup, dataPath;
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