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The search processing with help JavaScript

readyState property XMLHttpRequest - numerical value which defines{determines} the status of a cycle of search. It changes from 0 for "uncertain" and up to 4 for "completed". Each time when varies readyState, appears event readystatechange and the operator is caused with the help onreadystatechange properties.

In listing 3 you have seen, how function getReadyStateHandler () for creation of the operator was caused. This operator then is attributed to property onreadystatechange. getReadyStateHandler () used that fact, that functions - objects of the first class in JavaScript. It designates, that functions can be parameters to other functions and can create and return values of other functions also. To a duty getReadyStateHandler () - to return value of function which checks, whether has come to the end XMLHttpRequest and whether the answer in a XML-format in the operator determined by a call has been sent. Listing 6 - a code for getReadyStateHandler ().

Listing 6. Function getReadyStateHandler ().

/*

                        * Returns function which expects that has ended

                        * Certain{Determined} XMLHttpRequest, then passes his{its} answer in a XML-format

                        * To the set operator * req is XMLHttpRequest, whose status changes

                        * responseXmlHandler - the function, transmitted search XML

                        */

                        function getReadyStateHandler (req, responseXmlHandler) {

// Returns uncertain function which reads out

// Data XMLHttpRequest return function () {

// If the status is required "is finished"

if (req.readyState == 4) {

// We check, whether there has come the successful answer of the server

if (req.status == 200) {

// Passes XML to the operator

responseXmlHandler (req.responseXML);

} else {

// There was mistake HTTP

alert (" HTTP error: " +req.status);

}

}

}

}