Interface ContextEdit

Example

import { HumanMessage, type ContextEdit, type BaseMessage  } from "langchain";

class RemoveOldHumanMessages implements ContextEdit {
  constructor(private keepRecent: number = 10) {}

  async apply({ messages, countTokens }) {
    // Check current token count
    const tokens = await countTokens(messages);

    // Remove old human messages if over limit, keeping the most recent ones
    if (tokens > 50000) {
      const humanMessages: number[] = [];

      // Find all human message indices
      for (let i = 0; i < messages.length; i++) {
        if (HumanMessage.isInstance(messages[i])) {
          humanMessages.push(i);
        }
      }

      // Remove old human messages (keep only the most recent N)
      const toRemove = humanMessages.slice(0, -this.keepRecent);
      for (let i = toRemove.length - 1; i >= 0; i--) {
        messages.splice(toRemove[i]!, 1);
      }
    }
  }
}
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