Use postmessage to report, Failed to execute 'postMessage' on' DOMWindow'

use postMessage to send cross-domain messages,
window.postMessage ("hello there messages, location.protocol +" / a.b.com") ;

but the following error was reported: 

Failed to execute "postMessage" on "DOMWindow": The target origin provided ("http://a.b.com") does not match the recipient window"s origin ("http://c.e.com")

what is the reason, please?

Javascript
Mar.23,2021

use event.source as reply object
for more information, please see https://developer.mozilla.org.

. 
//ApostMessagefunctionaddEventListenner
function receiveMessage(event)
{
  // 
  if (event.origin !== "http://example.com:8080")
    return;

  // event.source 
  // event.data  "hello there!"

  // origin (), enent.source
  // event.origintargetOrigin
  event.source.postMessage("hi there yourself!  the secret response " +
                           "is: rheeeeet!",
                           event.origin);
}

window.addEventListener("message", receiveMessage, false);

otherWindow.postMessage (message, targetOrigin, [transfer]);
otherWindow: A reference to other windows , such as the contentWindow property of iframe, the window object returned by window.open, or a named or numerically indexed window.frames.
otherWindow cannot be the current window.
see MDN

.

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MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1b36847-2c013.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1b36847-2c013.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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