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

javascript ajax xmlhttprequest readystate
Marius picture Marius · Mar 11, 2009 · Viewed 109.5k times · Source

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?

Answer

Kieron picture Kieron · Mar 11, 2009

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.

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