@plteam/chat-ui/dist/utils/observers/reaction.js

CUI Kit is a free and open-source library for creating AI assistant chat interfaces, built with React, Material UI, and TypeScript

export const reaction = (observableValue, callback, options) => {
    const disposer = observableValue.subscribe(() => {
        callback(observableValue.value);
    });
    if (options?.fireImmediately)
        callback(observableValue.value);
    return disposer;
};