Clash Royale CLAN TAG

Retain dynamically submitted select options on form submit

I have an html form with a dynamically populated select:

<form action="/" method="post" onsubmit="beforeSubmit()" id="crypto_form">
<textarea name="message" id="textarea_message" oninput="this.value.toUpperCase()" cols="60" rows="5" placeholder="Enter Message"></textarea>
<select form="crypto_form" name="keydata" id="select_keydata"></select>
<button type="submit" name="type" id="btn_encrypt" value="encrypt">Encrypt</button>
<button type="submit" name="type" id="btn_decrypt" value="decrypt">Decrypt</button>
</form>


The problem is that when I submit the form, all select values disappear. How do I retain them when I submit the form? I looked at similar questions to this, but none of them solve my particular case.

I'm using golang as a backend.

Note: The beforeSubmit() function is empty. Anything I can put in there to retain the options?

beforeSubmit()

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