PHP file how to get HTML JS data to solve the idea

How PHP files get HTML JS data
How the php file gets the HTML data, not the action.
To make long-term inquiries, such as hospitals and departments
It means there is a php file, a.php, there are two HTML files, hospital files: b.html and Department Files: c.html file. The action of the C file is submitted to the a.html file. But how a file to get the data of B file, this data exists in JS, passed to a file via JS
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You can put b.html content in the c.html and submit it in the past.
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I don't know what you mean, but a is going to write an Ajax method with the B-Exchange data.
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You this involves 3 pages, c.html submitted to b.html, then b.html how to operate it? Is it also a form submission? How does it relate to the a.php?
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Get b.html content in a.php

$b _html = file_get_contents (' b.html ');//This is the content of b.html

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