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Script only works while alert box is in the script

Answer 1

+2 A:

You should modify the plants variable in the callback function assigned to the onreadystatechange property.

xhr.onreadystatechange = function(){
    if(xhr.readyState==4 && xhr.status==200) {
        results = xhr.responseText;
        // Populate the "plants" variable here, then call a function
        // that does something with the plants variable.
    }
}

For more information: https://developer.mozilla.org/en/AJAX/Getting_Started

CalebD 2010-01-26 21:18:02

Answer 2

+1 A:

When you call

xhr.open("GET","db_interactions.php",true);

you are telling the XMLHttpRequest to operate asynchronously. You are telling it to go off and do its work, calling the callback function at some unspecified time in the future, when the request has been fully processed. Change that true to false, and it will work as you expect. On the other hand, that function might hang indefinitely in the event of a network slowdown, etc., so caveat programmor.

Jonathan Feinberg 2010-01-26 21:18:19

Answer 3

A:

XMLHttpRequest.send() is asynchronous. Without the alert the function runs faster than the ajax call and results is never initialized. You can fix this by changing the true in your open call to false to make it synchronous or set your global variable in your inline function

RHicke 2010-01-26 21:18:53

Answer 4

+1 A:

The callback function that sets the 'results' variable is asynchronous -- meaning that it will likely get set after the return statement, unless there's something to delay the return statement (e.g. an alert() call).

Drew Wills 2010-01-26 21:20:02

Answer 5

+5 A:

The reason it's not working is because the XmlHttpRequest is asynchronous. What this means is that you cannot do return results;

Here's a timeline, with your alert box:

Create XmlHttpRequest
Send it
Alert box pops up and sits there for a while
XmlHttpRequest result comes back and sets the results variable in your onreadystatechange function
You click OK on the alert box
the function returns (the return results line)
Other code runs and does things with the results variable.

Here's the timeline without the alert box:

Create XmlHttpRequest
Send it
the function returns (the return results line)
Other code runs and does things with the results variable. This fails because it hasn't been set yet
XmlHttpRequest result comes back and sets the results variable in your onreadystatechange function

Instead you have to put the plants code (splitting, etc) in the onreadystatechange callback, or put it in it's own function, and call that function from the onreadystatechange

Orion Edwards 2010-01-26 21:21:26

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Script only works while alert box is in the script

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