CODEWITHSUNDEEP
javascriptajaxxmlhttprequest
Boatmarker
Boatmarker

Reputation: 196

XMLHttpRequest event listeners order of execution

I have code retrieving some data using an XMLHttpRequest that looks something like this:

var myObject = new MyObject();
var req = new XMLHttpRequest();

req.addEventListener("load", function () {
    myObject.data = req.responseText;
}, false);

req.addEventListener("loadend", function () {
    myObject.save();
}, false);

req.open("GET", "http://www.example.com/foo.txt", true);
req.send(null);

Basically, if the Ajax request succeeds, I want to save the data retrieved in myObject, and then regardless of the status of the Ajax request, I want to save myObject to the database. So far it's worked as it's intended to, but I'm slightly uneasy about the order of execution of the load and loadend listeners. The most I could find on this was from the XMLHttpRequest living standard (regarding loadend):

After one of error, abort, timeout or load has been dispatched.

Does this guarantee that if the Ajax request succeeds, that the load listener will finish executing before the loadend listener starts?

Upvotes: 2

Views: 2840

Answers (1)

Bergi
Bergi

Reputation: 664971

order of execution of the load and loadend listeners

As you can judge from the standard, loadend will always be dispatched after load or the respective error event.

Does this guarantee that if the Ajax request succeeds, that the load listener will finish executing before the loadend listener starts?

JavaScript is single-threaded, with a run-to-completion event loop. Two listeners will never run at the same time.

Upvotes: 3

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