A Taskcluster client library for the browser
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Taskcluster Client Web

A Taskcluster client library for the browser.

This client library is generated from the auto-generated API reference. taskcluster-client-web differs from taskcluster-client by providing a version that is compatible with the browser out of the box and does not require a build step to use.


You can install this package using Yarn, npm, or include via script tags:

Yarn installation

yarn add taskcluster-client-web

NPM installation

npm install --save taskcluster-client-web

Script installation

<script src="path/to/taskcluster-client-web.js"></script>

<!-- You can also include it from the unpkg CDN -->
<script src="https://unpkg.com/taskcluster-client-web"></script>

<!-- or from the jsDelivr CDN -->
<script src="https://cdn.jsdelivr.net/npm/taskcluster-client-web/lib/index.js"></script>

Note: taskcluster-client-web depends on 2 external packages: hawk and query-string. You must manually include these if you choose to use the script installation:

<script src="https://unpkg.com/hawk/lib/browser.js"></script>
<!-- or from the jsDelivr CDN -->
<script src="https://cdn.jsdelivr.net/npm/hawk/dist/browser.js"></script>
// hawk's "browser" client doesn't expose itself on window
window.hawk = hawk;
<script src="https://wzrd.in/standalone/query-string"></script>

<script src="https://unpkg.com/taskcluster-client-web"></script>
<!-- or from the jsDelivr CDN -->
<script src="https://cdn.jsdelivr.net/npm/taskcluster-client-web/lib/index.js"></script>


After installing this package, you can then import functionality as desired. Your specific build process and installation method will determine how you can import this functionality. The following importing standards are supported:

ES imports

import * as taskcluster from 'taskcluster-client-web';
import { Queue } from 'taskcluster-client-web';

CommonJS require

const taskcluster = require('taskcluster-client-web');
const { Queue } = require('taskcluster-client-web');

AMD/UMD require

require(['taskcluster-client-web'], (taskcluster) => {
  // ...

require(['taskcluster-client-web'], ({ Queue }) => {
  // ...

Global variable from script tag

<script src="path/to/taskcluster-client-web.js"></script>
  const taskcluster = window.taskcluster;

  const { Queue } = taskcluster;

Calling API Endpoints

To invoke an API endpoint, instantiate a taskcluster client class. In the following example we instantiate an instance of the Queue client class and use it to create a task.

Note: while these examples use ES imports, your actual usage will depend on what your build process or installation method support.

import { Queue } from 'taskcluster-client-web';

const taskId = '...';

// Instantiate the Queue Client class
const queue = new Queue({
  rootUrl: 'https://taskcluster.net',
  timeout: 30 * 1000, // timeout for _each_ individual http request
  credentials: {
    clientId: '...',
    accessToken: '...',
    // Certificate must also be provided if using temporary credentials,
    // this can be either a JSON object or a JSON string.
    certificate: {...} // Only applicable for temporary credentials

// Create task using the queue client
  .createTask(taskId, payload)
  .then((result) => {
    // status is a task status structure

The payload parameter is always a JavaScript object as documented by the REST API documentation. The methods always returns a promise for the response JSON object as documented in the REST API documentation. If you have JavaScript Async Function support, you can also await these methods.

If you need to create a client similar to a existing client, but with some options changed, use client.use(options):

  .use({ authorizedScopes: [/* ... */] })
  .createTask(/* ... */)
  .then(/* ... */);

This replaces any given options with new values.

Web Listener

Many Taskcluster components publish messages about current events to Pulse. The JSON reference object also contains metadata about declared Pulse exchanges and their routing key construction. This is designed to make it easy to construct routing key patterns and parse routing keys from incoming messages.

The following example creates a listener by creating a WebListener, as well as creating a QueueEvents instance which we use to find the exchange and create a routing pattern to listen for the completion of a specific task. The taskCompleted method will construct a routing key pattern by using * or # for missing entries, depending on whether or not they are single-word or multi-key entries.

By default the WebListener will connect to events.taskcluster.net using a WebSocket.

import { QueueEvents, WebListener } from 'taskcluster-client-web';

const queueEvents = new QueueEvents({ rootUrl });
const listener = new WebListener({
  credentials: {
    username: '...', // Pulse username from pulse guardian
    password: '...' // Pulse password from pulse guardian

// This binds to taskCompleted events from the queue
// that match routing key pattern:
// 'primary.<myTaskId>.*.*.*.*.*.#'
listener.bind(queueEvents.taskCompleted({ taskId: '<myTaskId>' }));

// Create an event handler to react to messages
listener.on('message', (message) => {
  message.exchange; // Exchange from which message came
  message.payload; // Documented on docs.taskcluster.net
  message.routingKey; // Message routing key in string format
  message.routing.taskId; // Element from parsed routing key
  message.routing.runId; // ...
  message.redelivered; // True if message has been nack'ed and requeued
  message.routes; // List of CC'ed routes, without the `route.` prefix

// Connect the listener
  .then(() => {
    // Listener is connected and listening for messages)

To bind to a custom routing-key like the task-specific routes that messages from the queue are CC'ed to, just provide the desired routing key to the method for exchange.

const rawRoutingPattern = 'route.task.specific.routing.key';


The WebListener accepts a few options for modifying its operation:

new WebListener({
  rootUrl: 'https://taskcluster.net',
  // By default the WebSocket will attempt to
  // reconnect every 5 seconds in case of disconnection
  reconnectInterval: 5000

The WebListener emits several events which can be reacted to using the on method:

listener.on(eventName, handler)

The handler is a function to be invoked every time a particular eventName event occurs, and can receive a JSON-parsed payload or error as an argument.

The eventName should correspond to one of the possible events the listener emits:

event Description
ready A socket connection has been established and can start transmitting messages.
message A message has been received from the service. The message will be parsed from JSON or be null and provided to the event handler.
bind The service has accepted a request to respond to a routing pattern. The response will be parsed from JSON or be null and provided to the event handler.
error A problem occurred while connecting or receiving a message. Can return metadata about the error or an Error instance to the event handler.
close The socket was disconnected. May occur more than once to account for reconnects.
reconnect The socket was re-connected after experiencing a close.

The return value of on() is a function which can be used to automatically unbind the event.

const removeListener = listener.on('close', () => console.log('CLOSED!'));

// ...

removeListener(); // The previous close event is no longer bound

You may also use the off() method to manually unbind a handler from an event.

const handleClose = () => console.log('CLOSE!');

listener.on('close', handleClose);

// ...

listener.off('close', handleClose);

The unbinding can also be done internally to the handler that is bound, allowing a handler to unbind itself if necessary. The easiest technique for doing this is to use a named function expression:

listener.on('close', function handler() {
  listener.off('close', handler);
  // ...

Once the WebListener has established a connection, it will check every 5 seconds to ensure the listener is still connected. To make the listener close its connect and halt reconnection attempts, call close().

const listener = new WebListener();

// ...

  .then(() => {
    // listener has disconnected and will not attempt
    // to reconnect

For convenience, there are also some methods to determine the status of the socket connection:

const listener = new WebListener({ rootUrl });

// This will return a Boolean based on whether the socket connection is in the OPEN state.

// This will return a Boolean based on whether the socket connection is currently connected.


Documentation for the set of API entries is generated from the built-in references, and is listed in the docs directory of this repository. Detailed documentation with description, payload, and result format details is available on this cluster's documentation site.

Providing Options

Some API end-points may take a query string. This is indicated in the signature as [options]. These options are always optional, commonly used for continuation tokens when paging a list.

Construct URLs

You can build a URL for any request, but this feature is mostly useful for requests that do not require any authentication. If you need authentication, take a look at the section on building signed URLs, which is possible for all GET requests. To construct a URL for a request use the buildUrl method, as illustrated in the following example:

import { Queue } from 'taskcluster-client-web';

// Create queue instance
const queue = new Queue({ rootUrl });

// Build url to get a specific task
const url = queue.buildUrl(
  queue.getTask,    // Method to build url for.
  taskId            // First parameter for the method, in this case taskId

Please note that the payload parameter cannot be encoded in URLs and must be sent when using a constructed URLs. This should not a problem as most methods that accept a payload also require authentication.

Construct Signed URLs

It's possible to build signed URLs for GET requests. A signed URL contains a query string parameter called bewit. This parameter holds expiration time, signature, and scope restrictions if applied. The signature covers the following parameters:

  • Expiration time,
  • URL and query string
  • Scope restrictions, if applied

These signed URLs are convenient if you want to grant someone access to a specific resource without proxying the request or sharing your credentials. It's fairly safe to provide someone with a signed URL for a specific artifact that is protected by a scope, for example:

import { Queue } from 'taskcluster-client-web';

// Create queue instance
const queue = new Queue({ rootUrl, credentials });

// Build signed url
    queue.getArtifactFromRun, // method to build signed url for.
    taskId, // Task ID parameter
    runId, // Run ID parameter
    artifactName, // Artifact name parameter
    { expiration: 60 * 10 }  // Expiration time in seconds
  .then(signedUrl => { /* ... });

NOTE: This method returns a promise, unlike in taskcluster-client.

Please note that the payload parameter cannot be encoded in the signed URL and must be sent as request payload. This should work fine, just remember that it's only possible to make signed URLs for GET requests, which in most cases don't accept a payload.

Also please consider using a relatively limited expiration time, as it's not possible to retract a signed url without revoking your credentials. For more technical details on signed urls, see bewit URLs in hawk.

Generating Temporary Credentials

If you have non-temporary Taskcluster credentials you can generate a set of temporary credentials as follows. Notice that the credentials cannot last more than 31 days, and you can only revoke them by revoking the credentials that were used to issue them, which can take up to one hour.

import { createTemporaryCredentials } from 'taskcluster-client-web';

const credentials = createTemporaryCredentials({
  // Name of temporary credential (optional)
  clientId: '...',
  // Validity of temporary credentials starts here
  start: new Date(),
  // Expiration of temporary credentials
  expiry: new Date(new Date().getTime() + 5 * 60 * 1000),
  // Scopes to grant the temporary credentials
  scopes: ['ScopeA', 'ScopeB', /* ... */],
  credentials: { // Non-temporary taskcluster credentials
    clientId: '...',
    accessToken: '...'

You cannot use temporary credentials to issue new temporary credentials. You must have auth:create-client:<name> to create a named temporary credential, but unnamed temporary credentials can be created regardless of your scopes.

Configuration of API Invocations

There are a number of configuration options for clients which affect invocation of API endpoints. These are useful if using a non-default server, e.g. when setting up a staging area or testing locally.

Configuring API Root URLs

If you use the built-in API client classes, you must configure the rootUrl when creating an instance of the client. As illustrated below:

import { Auth } from 'taskcluster-client-web';

const auth = new Auth({
  rootUrl: 'http://localhost:4040', // Useful for development and testing
  credentials: { /* ... */ },

Configuring Credentials

When creating an instance of a client class, the credentials can be provided in options. For example:

import { Auth } from 'taskcluster-client-web';

const auth = new Auth({
  credentials: {
    clientId: '...',
    accessToken: '...'

This is common server-side when using taskcluster-client, but for web applications the credentials are usually acquired through some user-login process. For such cases, the client uses a credentialAgent to get Taskcluster credentials corresponding to the logged-in user. Agents can be shared between multiple clients, and are inherited via .use.


This cluster's login service provides credentials in exchange for an OIDC access_token. To use this functionality, construct an OIDCCredentialAgent and pass it to the client. This agent will automatically fetch credentials as needed.

import { Queue, OIDCCredentialAgent } from 'taskcluster-client-web';

const credentialAgent = new OIDCCredentialAgent({
  accessToken: '...',

const queue = new Queue({ rootUrl, credentialAgent });

  .createTask(/* ... */)
  .then(/* ... */);

To get credentials from the agent, call its getCredentials method:

let credentials = await credentialAgent.getCredentials()

When the access token is refreshed, simply update it on the credential agent:

credentialAgent.accessToken = newAccessToken;

Other Credential Agents

Any object with an async getCredentials() method that returns Taskcluster credentials is suitable as a credential agent. The method will be called for every Client method call, so it should perform some local caching.

Restricting Authorized Scopes

If you wish to perform requests on behalf of a third-party that has a smaller set of scopes than you do, you can specify which scopes your request should be allowed to use with authorizedScopes. This is useful when the scheduler performs a request on behalf of a task group, or when authentication takes place in a trusted proxy. For example:

import { Queue } from 'taskcluster-client-web';

// Create a Queue Client class can only define tasks for a specific workerType
const queue = new Queue({
  // Credentials that can define tasks for any provisioner and workerType.
  credentials: {
    clientId: '...',
    accessToken: '...'
  // Restricting this instance of the Queue client to only one scope
  authorizedScopes: ['queue:post:define-task/my-provisioner/my-worker-type']

// This request will only be successful if the task posted is aimed at
// "my-worker-type" under "my-provisioner".
  .defineTask(taskId, taskDefinition)
  .then(result => {
    // ...

Configuration of Exchange Bindings

When a taskcluster client class is instantiated, the option exchangePrefix may be given. This will replace the default exchangePrefix. This can be useful if deploying a staging area or similar. For example:

import { QueueEvents } from 'taskcluster-client-web';

// Instantiate the QueueEvents Client class
const queueEvents = new QueueEvents({
  exchangePrefix: 'staging-queue/v1/'

// This listener will now bind to: staging-queue/v1/task-completed
listener.bind(queueEvents.taskCompleted({ taskId: '<myTaskId>' }));

Relative Date-Time Utilities

Many Taskcluster APIs require ISO 8601 timestamp offsets into the future as way of providing expiration, deadlines, etc. These can be easily created using new Date().toJSON(), however, it can be rather error prone and tedious to offset Date objects into the future. Therefore this library comes with two utility functions for this purpose.

import { fromNow, fromNowJSON } from 'taskcluster-client-web';

const dateObject = fromNow('2 days 3 hours 1 minute');
const dateString = fromNowJSON('2 days 3 hours 1 minute');

(dateObject.toJSON() === dateString)
// dateObject = now() + 2 days 2 hours and 1 minute
(new Date().getTime() < dateObject.getTime())

By default it will offset the datetime into the future. If the offset strings are minus-prefixed (-), the date object will be offset into the past. This is useful in some corner cases.

import { fromNow } from 'taskcluster-client-web';

const dateObject = fromNow('- 1 year 2 months 3 weeks 5 seconds');

// dateObject = now() - 1 year, 2 months, 3 weeks and 5 seconds
(new Date().getTime() > dateObject.getTime())

The offset string is ignorant of whitespace and case-insensitive. It may also optionally be plus-prefixed +, if not minus-prefixed. Any + prefix will be ignored. However, entries in the offset string must be given in order from highest to lowest, e.g. 2 years 1 day. Additionally, various shorthands may be employed, as illustrated below.

  years,    year,   yr,   y
  months,   month,  mo
  weeks,    week,   wk,   w
  days,     day,          d
  hours,    hour,   hr,   h
  minutes,  minute, min
  seconds,  second, sec,  s

The fromNow function may also be given a date to be relative to as a second argument. This is useful if offsetting the task expiration relative to the the task deadline or doing something similar.

import { fromNow } from 'taskcluster-client-web';

const dateObject1 = fromNow('2 days 3 hours');
// dateObject1 = now() + 2 days and 3 hours

const dateObject2 = fromNow('1 year', dateObject1);
// dateObject2 = now() + 1 year, 2 days and 3 hours

Handling Credentials

Your users may find the options for Taskcluster credentials overwhelming. You can help by interpreting the credentials for them.

The credentialInformation(credentials, options) function returns a Promise with information about the given credentials:

   clientId: '..', // name of the credential
   type: '..', // type of credential, e.g., "temporary"
   active: '..', // active (valid, not disabled, etc.)
   start: '..', // validity start time (if applicable)
   expiry: '..', // validity end time (if applicable)
   scopes: ['...'] // associated scopes (if available)

The resulting information should only be used for presentation purposes, and never for access control. This function may fail unexpectedly with invalid credentials and performs no cryptographic checks. It is acceptable to use the scopes result to determine whether to display UI elements associated with a particular scope, as long as the underlying API performs more reliable authorization checks.

Generating slug IDs

In Node.js you can rely on the slugid module to generate slug IDs, but in the browser we expose the preferred slug ID generation function as slugid().

import { slugid } from 'taskcluster-client-web';

// Generate new taskId
const taskId = slugid();

The generates nice random slug IDs.

Updating Built-In APIs

When releasing a new version of taskcluster-client-web library, you should always re-build the project using yarn build. There are also several other scripts for maintenance:

  • yarn update-all: Pull the latest API manifest, re-build the package, and update all documentation.
  • yarn build: Re-build the library for distribution.
  • yarn docs: Generate the API documentation Markdown files from the API reference.
  • yarn compile-clients: Pull the latest API manifest from the schema endpoint and re-create the client classes.
  • yarn list-clients: Print a list of client APIs built into taskcluster-client-web based on the API reference.
  • yarn show-client <client>: Print the detailed schema information for a particular client, e.g. yarn show Auth.
  • yarn test: Run the test suites.
  • yarn lint: Manually lint the source code of the repo.


taskcluster-client-web is released as MPL 2.0.