LanguageModel: prompt() method

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The prompt() method of the LanguageModel interface sends input to the language model and returns a Promise that resolves with the model's complete response as a string.

Syntax

js
prompt(input)
prompt(input, options)

Parameters

input

The content to prompt the model with. This is either:

options Optional

Options for creating a prompt. Properties include:

responseConstraint

An object following the structure defined by JSON Schema defining the precise format the model's output should be delivered in. When provided and omitResponseConstraintInput is false, any implementation-defined constraint-description message is included in the measurement.

omitResponseConstraintInput

A boolean; when true, the automatic constraint-description message is excluded from the measurement.

signal

An AbortSignal to cancel the operation.

Return value

A Promise that resolves with a String containing the model's complete response.

Exceptions

AbortError DOMException

Thrown if the operation was cancelled via the signal option.

NotAllowedError DOMException

Thrown if usage of the method is blocked by a language-model Permissions-Policy.

NotSupportedError DOMException

Thrown if:

OperationError DOMException

Thrown if the prompt fails for any other reason not listed in the other exception types.

QuotaExceededError DOMException

Thrown if the prompt would cause the session's context usage to exceed the model's LanguageModel.contextWindow.

SyntaxError DOMException

Thrown if:

TypeError

Thrown if:

Description

The prompt() method is the primary mechanism for interacting with a language model session. It adds the provided input to the context window and generates a response. The entire response is buffered and returned as a single string when generation completes.

For long responses or streaming use cases, use LanguageModel.promptStreaming() instead to receive the response incrementally. To add content to the context window without generating a response, use LanguageModel.append().

Each call to prompt() adds to the session's context. To branch from a given state without affecting the original session, call LanguageModel.clone().

Examples

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Basic text prompt

This example shows basic prompt() usage with a single user text input.

js
const session = await LanguageModel.create();
const response = await session.prompt(
  "Summarize the water cycle in one paragraph.",
);
console.log(response);

See also Using the Prompt API > Prompting the model.

Multi-turn conversation

js
const session = await LanguageModel.create();

const reply1 = await session.prompt("My name is Alex.");
console.log(reply1); // "Nice to meet you, Alex!"

const reply2 = await session.prompt("What's my name?");
console.log(reply2); // "Your name is Alex."

Constrained JSON output

The following example shows how do pass JSON to the responseConstraint option to specify that you want an array returned by the call to prompt().

js
const session = await LanguageModel.create();
const raw = await session.prompt("Name three planets in our solar system.", {
  responseConstraint: {
    type: "object",
    properties: {
      planets: {
        type: "array",
        items: { type: "string" },
      },
    },
    required: ["planets"],
  },
});

const { planets } = JSON.parse(raw);
console.log(planets); // ["Mercury", "Venus", "Earth"]

See also Adding context with initial and ongoing prompt inputs > Adding response constraints.

Cancelling a prompt

The following example shows how to enable a user to cancel a prompt with a button. It does this by creating an AbortController. Its abort() is callable from a button's click handler. For this to work, a reference to the controller's signal property must be passed to prompt().

js
const controller = new AbortController();

// Select your cancel button from the DOM
const cancelButton = document.querySelector("#btn-cancel");

// Trigger the abort when the user clicks the button
cancelButton.addEventListener("click", () => {
  controller.abort();
});

try {
  const response = await session.prompt("write a very long story.", {
    signal: controller.signal,
  });
  console.log(response);
} catch (err) {
  if (err.name === "AbortError") {
    console.log("prompt was cancelled.");
  } else {
    console.error("An unexpected error occurred:", err);
  }
}

See also Using the Prompt API > Cancelling operations and destroying instances.

Specifications

See also