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Asked: 2026-05-10T17:31:10+00:00

Is there a documented max to the length of the string data you can

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Is there a documented max to the length of the string data you can use in the send method of an XMLHttpRequest for the major browser implementations?

I am running into an issue with a JavaScript XMLHttpRequest Post failing in FireFox 3 when the data is over approx 3k. I was assuming the Post would behave the same as a conventional Form Post.

The W3C docs mention the data param of the send method is a DOMString but I am not sure how the major browsers implement that.

Here is a simplified version of my JavaScript, if bigText is over about 3k it fails, otherwise it works…

var xhReq = createXMLHttpRequest();  function createXMLHttpRequest() {   try { return new ActiveXObject('Msxml2.XMLHTTP'); } catch (e) {}   try { return new ActiveXObject('Microsoft.XMLHTTP'); } catch (e) {}   try { return new XMLHttpRequest(); } catch(e) {}   alert('XMLHttpRequest not supported');   return null; }  function mySubmit(id, bigText) {   var url    = 'SubmitPost.cfm';   var params = 'id=' + id + '&bigtext=' + encodeURI(bigText);    xhReq.open('POST', url, true);    //Send the header information along with the request   xhReq.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');   xhReq.setRequestHeader('Content-length', params.length);   xhReq.setRequestHeader('Connection', 'close');    xhReq.onreadystatechange = onPostSubmit;   xhReq.send(params); }  function onPostSubmit() {    if (xhReq.readyState==4 || xhReq.readyState=='complete')      {       if (xhReq.status != 200)         {         alert('BadStatus');         return;         }     }  }
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1 Answer

  1. I believe the maximum length depends not only on the browser, but also on the web server. For example, the Apache HTTP server has a LimitRequestBody directive which allows anywhere from 0 bytes to 2GB worth of data.

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