How to find out upload/post time of an special website URL?

Often when searching for information i hit the problem, that the author of an article/website/blog post doesnt give out a date.

Is there any way (maybe special meta search engine, web-archives, use of google search operators to find out at least on which month & year a website UR开发者_StackOverflow中文版L was uploaded?

thx

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puttin

javascript:alert(document.lastModified)

in the adress bar of a browser with loaded page pops up a date and time. Where this time data is coming from i have no idea, probably time html or php file was created on server. On the other way i thought javascript cannot access filesystem, but im no expert...

Still curious if someone knows a reliable method of finding out when a specific .html site was created as i find it useful for enquiry.