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

Question

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

User · Answer

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

User · Answer

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 · Answer

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 · Answer

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

User · Answer

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

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

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