LanguageModel: prompt() method

Syntax

prompt(input)
prompt(input, options)

Parameters

input

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

• A string — Shorthand for a single textual message.
• An array of objects, each representing a single message in a conversation with a language model. Objects may have the following properties:

  role

  A string indicating the point of view the message is phrased from. Must be one of:

  system

  A system-level instruction that guides the model's overall behavior. This must be the first instruction passed to the model.

  user

  A message from the user, which the API should respond to.

  assistant

  An input that provides context for the AI assistant, such as its persona or the format of its responses. Such messages mainly serve to provide context/history, and further shape how the model responds.

  content

  A string representing a textual prompt, or an array of objects. Each object includes the following properties:

  type

  An enumerated value representing the type of content. This can be one of:

  audio

  Audio content.

  image

  Image content.

  text

  Textual content.

  tool-call

  A tool invocation issued by the model.

  tool-response

  The result of a tool invocation.

  value

  The content of the message. If the type is text, this is always a string. If the type is audio or image, the value can be one of several different object types; see What data types are accepted?.

  prefix Optional

  A boolean, defaulting to false. When true, the message is treated as a prefix for the model's next generated response rather than a complete turn.

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:

• A message's role is assistant and its type is anything other than text.
• A message's type is text and its value is not a string.
• The input or output text is in a language the user agent doesn't support for prompting.
• A message's type is image or audio but the type was not listed in expectedInputs, or the value is not an accepted data type.

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:

• No messages are included in the messages array.
• A message's prefix property is set to true and:
  • The message's role is not assistant.
  • The message is not the last item in the messages array.

TypeError

Thrown if:

• omitResponseConstraintInput is true but responseConstraint is not provided.
• A message's role is system but it was not the first message passed to the context.

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

Basic text prompt

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

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

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().

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().

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

Browser compatibility

See also

• LanguageModel.promptStreaming()
• LanguageModel.append()
• Prompt API
• Using the Prompt API
• Adding context with initial and ongoing prompt inputs