What do the different readystates in XMLHttpRequest mean, and how can I use them?

Marius_1585 0
Viewed 110999

XMLHttpRequest has 5 readyStates, and I only use 1 of them (the last one, 4).

What are the others for, and what practical applications can I use them in?

readystate xmlhttprequest ajax javascript
5 Answers

The full list of readyState values is:

State  Description
0      The request is not initialized
1      The request has been set up
2      The request has been sent
3      The request is in process
4      The request is complete

(from https://www.w3schools.com/js/js_ajax_http_response.asp)

In practice you almost never use any of them except for 4.

Some XMLHttpRequest implementations may let you see partially received responses in responseText when readyState==3, but this isn't universally supported and shouldn't be relied upon.

user_5880

Original definitive documentation

0, 1 and 2 only track how many of the necessary methods to make a request you've called so far.

3 tells you that the server's response has started to come in. But when you're using the XMLHttpRequest object from a web page there's almost nothing(*) you can do with that information, since you don't have access to the extended properties that allow you to read the partial data.

readyState 4 is the only one that holds any meaning.

(*: about the only conceivable use I can think of for checking for readyState 3 is that it signals some form of life at the server end, so you could possibly increase the amount of time you wait for a full response when you receive it.)

user_189360
  • 0 : UNSENT Client has been created. open() not called yet.
  • 1 : OPENED open() has been called.
  • 2 : HEADERS_RECEIVED send() has been called, and headers and status are available.
  • 3 : LOADING Downloading; responseText holds partial data.
  • 4 : DONE The operation is complete.

(From https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest/readyState)

user_66900020
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