LanguageModel: clone() method
Limited availability
This feature is not Baseline because it does not work in some of the most widely-used browsers.
Secure context: This feature is available only in secure contexts (HTTPS), in some or all supporting browsers.
The clone() method of the LanguageModel interface creates a copy of the LanguageModel it is called on, including its full context window state. The cloned session can be used independently without affecting the original.
The original and the clone share the same context history up to the point of cloning, enabling you to explore multiple response paths or test variations without starting from scratch.
For example, you might build a shared context using append() or early prompt() prompt() calls, clone the session, and then send different follow-up prompts to each clone in parallel.
Syntax
clone()
clone(options)
Parameters
optionsOptional-
An object representing the options that can be passed. If this argument is absent, the
optionsfrom the original session, such as its abort signal, are used. Properties include:signal-
An
AbortSignalto cancel the clone operation.
Return value
A Promise that resolves with a cloned LanguageModel instance.
Exceptions
AbortErrorDOMException-
Thrown if the operation was cancelled via the
signaloption. NotAllowedErrorDOMException-
Thrown if usage of the method is blocked by a
language-modelPermissions-Policy. OperationErrorDOMException-
Thrown if cloning fails for any other reason not listed in the other exception types.
Examples
See also Using the Prompt API > Cloning a session.
Exploring multiple response paths
The following example shows how to explore different response paths. First, it creates a single session with the start of a story. Then it clones the original session twice before prompting for different endings. This approach preserves the original session in case more exploration is wanted.
const session = await LanguageModel.create({
initialPrompts: [
{ role: "system", content: "You are a creative writing assistant." },
],
});
await session.append(
"The story begins in a small coastal town during a storm.",
);
const [clone1, clone2] = await Promise.all([session.clone(), session.clone()]);
const [ending1, ending2] = await Promise.all([
clone1.prompt("Write a happy ending."),
clone2.prompt("Write a mysterious ending."),
]);
console.log("Happy ending:", ending1);
console.log("Mysterious ending:", ending2);
Cloning to retry after a context overflow
This example uses a checkpoint and rollback pattern to save the state of a session before attempting to append a large amount of data. Cloning the session before calling append() allows the app to restore the state if the context window is exceeded.
const veryLargeDocument = "This is my very long story...";
let session = await LanguageModel.create();
const checkpoint = await session.clone();
try {
await session.append(veryLargeDocument);
} catch (err) {
if (err.name === "QuotaExceededError") {
console.warn("Document too large.");
session = checkpoint;
}
}
Cloning a session with an abort signal
The following example creates a timeout to abort the clone operation if it takes more than three seconds.
const controller = new AbortController();
setTimeout(() => controller.abort(), 3000);
try {
const clonedSession = await session.clone({
signal: controller.signal,
});
console.log("Session cloned successfully.");
} catch (err) {
if (err.name === "AbortError") {
console.log("Clone operation was aborted.");
}
}
Specifications
| Specification |
|---|
| Prompt API # dom-languagemodel-clone |