Question about $ _ server ["http_host "]

For more information, see $ _ server [& quot; http_host & quot;]. The website address is test.com. we didn't use $ _ server [& quot; http_host & quot;] in IE. obtain the current URL. the output is compatible. if www is added before the URL, ask $ _ server ["http_host"] when the URL is www.test.com.
The URL is test.com, and there is no www

In IE, use $ _ server ["http_host"] to obtain the current URL. the output is a compatible string.
If you add www to the front of the website, you can get the website address correctly when the website address is www.test.com.

It is normal in Firefox and google browsers.

------ Solution --------------------
Impossible. How can php be related to ie...
------ Solution --------------------
What the landlord said...
------ Solution --------------------
No. post the code. How can php be related to ie.

Discussion

Reference:

Impossible. How can php be related to ie...

Is to get the current URL
In ie, if there is no www before the website, the correct website cannot be obtained.
But Firefox can

------ Solution --------------------
Discussion

Thank you for your attention.
It is expected that two variables in the background are used directly without definition. the results cannot be executed in IE, but Firefox can.

It seems that the frontend and backend of JS should not be lazy and omit the definition of variables.