Add code to the invoke() function of class BaseChatModel to move the finish_reason from the chatGeneration to the additional_kwargs of the AIMessage sothat the finish_reason can be used for routing when it is returned by the model in a runnableSequence

[reemster123]

I was creating my own custom agent and wanted to create a route() function based on the models AImessage, but then i noticed that it is not possible to determine if the model returns an AgentFinish or not since we can not use instanceOf in NodeJS. Then i looked into the BaseChatModel class's invoke() function and indeed it still has a comment which says :
"// TODO: Remove cast after figuring out inheritance" at langchain/dist/chat_models/base.cjs line 50.

I did not figuere out inheritence but i found another way to atleast be able to return the "finish_reason" property without having to rework every related function or class. We could do this by adding the following lines:

const finish_reason = chatGeneration.generationInfo.finish_reason; chatGeneration.message.additional_kwargs.finish_reason = finish_reason;

This will get the finish_reason property from the defined chatGeneration object and move it to the additional_kwags object nested into the AImessage. In this way we could always look into the additional_kwargs to find the finish_reason and we don't have to change the type or structure of the Message the invoke() function returns.

In my own project i created a CustomChatOpenAI class which extends CHatOpenAI and i added these lines and now i'm able to use it in routing. Maybe it helps adding it here to ;)

example :

import { BaseChatModel } from "langchain/chat_models/base";

class CustomChatOpenAI extends ChatOpenAI {
async invoke(input, options) {
const promptValue = BaseChatModel._convertInputToPromptValue(input);
const result = await this.generatePrompt([promptValue], options, options?.callbacks);
const chatGeneration = result.generations[0][0];
// TODO: Remove cast after figuring out inheritance
// CUSTOM ADDED: get the finish_reason from the chatGeneration and move it to the additional_kwargs
const finish_reason = chatGeneration.generationInfo.finish_reason;
chatGeneration.message.additional_kwargs.finish_reason = finish_reason;

    return chatGeneration.message;
}

}

export { CustomChatOpenAI };