Why the server does not respond to my AJAX request?

IMPORTANT! I am a novice, just starting to learn asynchronous requests:)
My situation:
Trying to parshanut the price of a specific item on the TP Stim, if you type in the address bar of the browser the link to the JSON file for this item(from the console output), I successfully get this file, but if I try my function to send AJAX request, nothing comes out, the console viditsja error:
"Failed to load https://steamcommunity.com/market/priceoverview/?a... Response to a preflight request doesn't pass the access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'null' is therefore not allowed access."
As I understand, server doesn't like HTTP header, which has a "not" value, and the campaign browser does not allow this header to declare(or not?)
Do not understand anything, because the browser extension successfully sends the request, but why can't I? For me, this topic is pretty vague, to be solidary:)
Here, my attempt to fashion a query:
FUN_AjaxGet function(){
 var xhr = new XMLHttpRequest();
 xhr.open('GET', 'https://steamcommunity.com/market/priceoverview/?appid=753&country=RU¤cy=5&market_hash_name=425580-Chapter%202%20(Trading%20Card)',true);
//xhr.setRequestHeader('Access-Control-Allow-Origin','1'); //same header that your server tried to deliver value, but, like it's ad header is successfully ignored
//The header I copied from the console (advanced queries), some were not valid, had them removed.
 if(xhr.status!=200){alert(xhr.status+' : '+xhr.readyState+' [ Error ]');} // handle the error;
 else {alert(xhr.responseXML+' [ Zaebis ]');} // display the result;

If not difficult, explain briefly how to build the query in a function, what methods are required and what is responsible for what
June 3rd 19 at 19:33
1 answer
June 3rd 19 at 19:35
But if the domain is not the one from where the request is sent? - Telly.Luettgen commented on June 3rd 19 at 19:38
find out how in the scheme of cross-DOMAIN requests there is no domain ? :) - Mohamed_Lind75 commented on June 3rd 19 at 19:41
I don't know, the request function is activated on the local page, just located on your computer, I don't think she has a domain, do I need to put at least the local server, buy domain etc to send the request?) A browser extension somehow manages (although there are scripts that are triggered on a specific page, maybe that's it?) - Telly.Luettgen commented on June 3rd 19 at 19:44
the domain localhost - Mohamed_Lind75 commented on June 3rd 19 at 19:47
Then there is a problem that the server refuses to respond to such a domain? - Telly.Luettgen commented on June 3rd 19 at 19:50
Yes , the link go! which I gave you, there all is written :) - Mohamed_Lind75 commented on June 3rd 19 at 19:53

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