Hello. So I'm making something like a calculator using PHP, but the code becomes ugly as I place checking and type conversions everywhere to make it safe. But now I've got another idea. I have a really low experience of JS, but making some simple calculations with some logical operations can't be hard. But the problem is that I'm going to outpost some input data and the result on the screen.

The question would be. Is it safe (can someone hack my website using this (continue reading) to harm my website and/or its users) to allow writing the code on my website using that Javascript? Well, writing some security staff is pointless, I guess, because anyone can edit the code. And when you think about editing the code of the website, anyone, even I, can write any code on the website they are visiting, but it's not going to harm it as long as it's not saved in any database to be displayed by the server. The answer looks obvious, but, as I said earlier, my experience is really low on JS (and I hate scripting languages which makes my experience on them even lower) and I just want to be one hundred and one percent sure about that.

P.S. The question doesn't look hard to me, waiting for the answer.

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Sorry, didn't quite get that. Could you explain?

OK, There is a form in which you enter some numbers, mark something from a drop-down menu and then the page reloads sending all that data in POST. Then PHP makes some simple calculation and prints something on the screen. I do filter all the data so it doesn't contain any harmful code and then it calculates the answer using some formulas.

I want to use JS instead of PHP because then, I would save server resources (not a lot, but anyway) and those calculations are simple enough that the JavaScript wouldn't run too slowly. Actually it should be nearly instant. So the question is if it is safe to use JS to publish something on the website? I'm not going to save any of that data on my server, so it looks like it can't make any harm to the website, but I just want to be sure.

Example.
So I usually type some numebrs in the form:
90
14
3

and it makes some calculations using those three. Then it prints the answer:

4

So, I want to use JS for this as it is very simple, but JS is done in a browser and so anyone can edit the code, so it's totally unsecured against publishing code on the website:

90
< b > test </ b >
3.

During the calculations it may print some errors as the input is not a number, but anyway.

P.S. I just wonder if JS can make any harm to the website. I mean should I still use PHP or is JS OK?

------Edited------
Delete this thread, found out about such thing as innerText

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JS won't harm your web page as I believe you aren't doing any post back to the server.