What do the different readystates in XMLHttpRequest mean, and how can I use them?
JavascriptAjaxXmlhttprequestReadystateJavascript Problem Overview
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?
Javascript Solutions
Solution 1 - Javascript
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.
Solution 2 - Javascript
kieron's answer contains w3schools ref. to which nobody rely , bobince's answer gives link , which actually tells native implementation of IE ,
so here is the original documentation quoted to rightly understand what readystate represents :
> The XMLHttpRequest object can be in several states. The readyState attribute must return the current state, which must be one of the following values:
>
> UNSENT (numeric value 0)
> The object has been constructed.
>
> OPENED (numeric value 1)
> The open() method has been successfully invoked. During this state request headers can be set using setRequestHeader() and the request can be made using the send() method.
>
> HEADERS_RECEIVED (numeric value 2)
> All redirects (if any) have been followed and all HTTP headers of the final response have been received. Several response members of the object are now available.
>
> LOADING (numeric value 3)
> The response entity body is being received.
>
> DONE (numeric value 4)
> The data transfer has been completed or something went wrong during the transfer (e.g. infinite redirects).
Please Read here : W3C Explaination Of ReadyState
Solution 3 - Javascript
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.)
Solution 4 - Javascript
onreadystatechange Stores a function (or the name of a function) to be called automatically each time the readyState property changes readyState Holds the status of the XMLHttpRequest. Changes from 0 to 4:
0: request not initialized
1: server connection established
2: request received
3: processing request
4: request finished and response is ready
status 200: "OK"
404: Page not found
Solution 5 - Javascript
- 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)