Submitting POST Request only once

I've been looking for a very simple code to rate limit a form on HTML (I use Django as a backend).

I did not find a solution to disable a button once it has been submitted.

Let's see a simple example:

<form method="POST" action="{% url 'example' %}">
{% csrf_token %}

<input name="input" id="input-1" placeholder="Test Field">

<button type="submit" id="btn-1">Submit</button>
</form>

How can we use simple Javascript 'onclick' to disable the button once it's clicked?