如何使用JQuery / JavaScript / PHP将文本写入外部文件？

I have some text stored in a POST variable that I need to append to an HTML file. I want to do within my PHP webpage, but it could use HTML, JQuery, Javascript, or anything else that will run natively. I've tried the PHP approach, but it hasn't worked despite my numerous attempts. Always a 500 internal server error. And I can't find anything on writing to files using JQuery, so if anyone out there knows something I don't, it would be appreciated. Thanks :)

Writing directly to you html/php documents is extremely bad practice. As your comment said you need to validate the input and if you make a mistake you could screw up your whole website.

There are a couple of options you could use:

• localstorage: This saves the changes to the browser of the user. This means that the changes wont be on the server. Very easy solution.
  
• Add a database: With PHP it is very easy to add a SQL databse. Write some functions that write the data to the database and read the data from there. Safer than writing directly to HTML/PHP but still needs validation
  
• Do some extreme reading into all the PHP IO functions. You need some extreme good handling if you want this site live.

I think that with the DB you`ll manage, just be safe and build in some security