Therequest() method of theLockManager interface requests aLock object with parameters specifying its name and characteristics.The requestedLock is passed to a callback, while the function itself returns aPromise that resolves (or rejects) with the result of the callback after the lock is released, or rejects if the request is aborted.

Themode property of theoptions parameter may be either"exclusive" or"shared".

Request an"exclusive" lock when it should only be held by one code instance at a time.This applies to code in both tabs and workers. Use this to represent mutually exclusive access to a resource.When an"exclusive" lock for a given name is held, no other lock with the same name can be held.

Request a"shared" lock when multiple instances of the code can share access to a resource.When a"shared" lock for a given name is held, other"shared" locks for the same name can be granted, but no"exclusive" locks with that name can be held or granted.

This shared/exclusive lock pattern is common in database transaction architecture, for example to allow multiple simultaneous readers (each requests a"shared" lock) but only one writer (a single"exclusive" lock).This is known as the readers-writer pattern.In theIndexedDB API, this is exposed as"readonly" and"readwrite" transactions which have the same semantics.

Syntax

request(name, callback)request(name, options, callback)

Parameters

name

An identifier for the lock you want to request.

optionsOptional

An object describing characteristics of the lock you want to create.Valid values are:

modeOptional

Either"exclusive" or"shared".The default value is"exclusive".

ifAvailableOptional

Iftrue, the lock request will only be granted if it is not already held.If it cannot be granted, the callback will be invoked withnull instead of aLock instance.The default value isfalse.

stealOptional

Iftrue, then any held locks with the same name will be released, and the request will be granted, preempting any queued requests for it.The default value isfalse.

Warning:Use with care!Code that was previously running inside the lock continues to run, and may clash with the code that now holds the lock.

signalOptional

AnAbortSignal (thesignal property of anAbortController);if specified and theAbortController is aborted, the lock request is dropped if it was not already granted.

callback

Method called when the lock is granted.The lock is automatically released when the callback returns (or an exception is thrown).Usually the callback is an async function, which causes the lock to be released only when the async function has completely finished.

Return value

APromise that resolves (or rejects) with the result of the callback after the lock is released, or rejects if the request is aborted.

Exceptions

This method may return a promise rejected with aDOMException of one of the following types:

InvalidStateErrorDOMException

Thrown if the environments document is not fully active.

SecurityErrorDOMException

Thrown if a lock manager cannot be obtained for the current environment.

NotSupportedErrorDOMException

Thrown ifname starts with a hyphen (-), both optionssteal andifAvailable aretrue, or if optionsignal exists andeither optionsteal orifAvailable istrue.

AbortErrorDOMException

Thrown if the optionsignal exists and is aborted.

Examples

General Example

The following example shows the basic use of therequest() method with an asynchronous function as the callback.Once the callback is invoked, no other running code on this origin can holdmy_resource until the callback returns.

await navigator.locks.request("my_resource", async (lock) => {  // The lock was granted.});

mode example

The following example shows how to use themode option for readers and writers.

Notice that both functions use a lock calledmy_resource.ThedoRead() requests a lock in'shared' mode meaning that multiple calls may occur simultaneously across different event handlers, tabs, or workers.

async function doRead() {  await navigator.locks.request(    "my_resource",    { mode: "shared" },    async (lock) => {      // Read code here.    },  );}

ThedoWrite() function use the same lock but in'exclusive' mode which will delay invocation of therequest() call indoRead() until the write operation has completed.This applies across event handlers, tabs, or workers.

async function doWrite() {  await navigator.locks.request(    "my_resource",    { mode: "exclusive" },    async (lock) => {      // Write code here.    },  );}

ifAvailable example

To grab a lock only if it isn't already being held, use theifAvailable option.In this functionawait means the method will not return until the callback is complete.Since the lock is only granted if it was available, this call avoids needing to wait on the lock being released elsewhere.

await navigator.locks.request(  "my_resource",  { ifAvailable: true },  async (lock) => {    if (!lock) {      // The lock was not granted - get out fast.      return;    }    // The lock was granted, and no other running code in this origin is holding    // the 'my_res_lock' lock until this returns.  },);

signal example

To only wait for a lock for a short period of time, use thesignal option.

const controller = new AbortController();// Wait at most 200ms.setTimeout(() => controller.abort(), 200);try {  await navigator.locks.request(    "my_resource",    { signal: controller.signal },    async (lock) => {      // The lock was acquired!    },  );} catch (ex) {  if (ex.name === "AbortError") {    // The request aborted before it could be granted.  }}

Specifications

Browser compatibility