Langsmith Hub Javascript Inline doesn't work

[Mosquid]

Checked other resources

• I added a very descriptive title to this issue.
• I searched the LangChain.js documentation with the integrated search.
• I used the GitHub search to find a similar question and didn't find it.
• I am sure that this is a bug in LangChain.js rather than my code.
• The bug is not resolved by updating to the latest stable version of LangChain (or the specific integration package).

Example Code

const prompt = ChatPromptTemplate.fromMessages([
    ['system', 'You are a helpful assistant'],
    ['placeholder', '{chat_history}'],
    ['human', '{input}'],
    ['placeholder', '{agent_scratchpad}'],
  ]);

Error Message and Stack Trace (if applicable)

No response

Description

https://smith.langchain.com/hub/hwchase17/openai-functions-agent
The code in "Javascript Inline" here is broken.

This is the code provided on the template page:

import { ChatPromptTemplate } from "@langchain/core/prompts";

const prompt = ChatPromptTemplate.fromMessages(
  ["system", "You are a helpful assistant"],
  ["placeholder", "{chat_history}"],
  ["human", "{input}"],
  ["placeholder", "{agent_scratchpad}"],
)

It gives an error: "Expected 1-2 arguments, but got 4".

Based on the langchain docs, it should look like this:

const prompt = ChatPromptTemplate.fromMessages([
  ["system", "You are a helpful assistant"],
  ["placeholder", "{chat_history}"],
  ["human", "{input}"],
  ["placeholder", "{agent_scratchpad}"],
])

But with this modification, it gives a different error: "Missing value for input variable {chat_history}"

System Info

info.txt

[dosubot]

It looks like there's a misunderstanding in how the ChatPromptTemplate.fromMessages function is used in LangChain JS. The correct usage involves passing an array of BaseMessagePromptTemplate instances, each representing a message in the chat. Here's how you should structure your code:

import { ChatPromptTemplate, SystemMessagePromptTemplate, HumanMessagePromptTemplate } from "@langchain/core/prompts";

const prompt = ChatPromptTemplate.fromMessages([
  SystemMessagePromptTemplate.fromTemplate("You are a helpful assistant"),
  PlaceholderPromptTemplate.fromTemplate("{chat_history}"),
  HumanMessagePromptTemplate.fromTemplate("{input}"),
  PlaceholderPromptTemplate.fromTemplate("{agent_scratchpad}"),
]);

This approach uses SystemMessagePromptTemplate.fromTemplate and HumanMessagePromptTemplate.fromTemplate for system and human messages, respectively, and PlaceholderPromptTemplate.fromTemplate for placeholders.

Regarding the "Missing value for input variable {chat_history}" error, it indicates that the placeholder {chat_history} is being used without providing its actual value. Ensure you supply values for all placeholders when using the prompt.format function, like so:

const formattedPrompt = prompt.format({
  chat_history: "Previous chat history",
  input: "User's input",
  agent_scratchpad: "Agent's scratchpad",
});

This method replaces placeholders with their corresponding values, ensuring the prompt is correctly formatted.

For further examples and detailed guidance, consider checking the examples/src/prompts/prompts.ts file in the LangChain JS repository.

If there are any more questions or if something isn't clear, feel free to ask.

Sources

• chat-conversational-react-description is not working
• examples/src/prompts/load_from_hub.ts
• examples/src/prompts/prompts.ts

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[jacoblee93]

["placeholder", "{agent_scratchpad}"], isn't supported yet - @rahilvora this would be a good one to add!