Set trigger values for custom button components

Problem

As far as I know, it is not possible to set a one-time value using JavaScript Component API. The only method available is Streamlit.setComponentValue().

Thus, it is not possible to implement custom buttons easily.

Solution

In native widgets, setting a one-time value is done with setTriggerValue. It’d be great to have this function for components.

Additional context

This issue was already discussed here: https://discuss.streamlit.io/t/button-using-custom-component/7536. In this topic, I’ve provided a temporary solution which triggers two reruns after a button click.

Another temporary solution would be to rely on query parameters. But I haven’t tested this yet.

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[okld]

Another temporary solution using st.session_state:

import streamlit as st

def return_value_once():
    # Let's assume that slider is a custom component that returns the same value everytime
    new_value = st.slider("My component value", 1, 10)

    if "old_value" not in st.session_state or new_value != st.session_state.old_value:
        st.session_state.old_value = new_value
        return new_value

    return None

st.title("Return value only if changed")
st.write("Here is my value:", return_value_once())

[PablocFonseca]

Pushing this one up. I just got in the same situation of @andfanilo and @okld. Needed to implemnt a custom button like component and no other way besides setComponentValue and block component return in python.