fix(core): Add typing in ChatMessagePromptTemplate.fromTemplate

[gouroujo]

When using the static method fromTemplate, this PR allows the type of the input to be strictly enforced.

When using the following example :

  const chatPrompt = ChatPromptTemplate.fromTemplate<{foo: string, bar: string}>("Hello {foo}, I'm {bar}");
  const messages = await chatPrompt.formatPromptValue({
    foo: "Foo",
    bar: "Bar",
  });

If an input is missing you got a type error Property 'foo' is missing in type '{ bar: string; }' but required in type 'TypedPromptInputValues<{ foo: string; bar: string; }>'

I have reused the declarations found in PromptTemplate.fromTemplate with the eslint-disabled for the banned type Symbol to stay consistent.

Let me know if you have any feedback.

Thanks for the great work !

[vercel]

The latest updates on your projects. Learn more about Vercel for Git ↗︎

Name	Status	Preview	Comments	Updated (UTC)
langchainjs-docs	✅ Ready (Inspect)	Visit Preview		Mar 22, 2025 0:39am

1 Skipped Deployment

Name	Status	Preview	Comments	Updated (UTC)
langchainjs-api-refs	⬜️ Ignored (Inspect)			Mar 22, 2025 0:39am

[jacoblee93]

Thanks! You shouldn't have to do this in most cases but good to allow.