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  import taskclusterClientWeb from 'https://cdn.skypack.dev/taskcluster-client-web';


Taskcluster Client for Web

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A Taskcluster client library for the browser.

This library 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 or npm:

yarn add taskcluster-client-web
npm install --save taskcluster-client-web



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 }) => {
  // ...


To invoke an API endpoint, instantiate a taskcluster client class. In the following example we instantiate an instance of the Queue client class.

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

You must configure the rootUrl when creating an instance of the client. The credentials can also be provided in options. If no credentials are provided, requests will be made without authentication.

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.

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.

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:create-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".
  .createTask(taskId, taskDefinition)
  .then(result => {
    // ...

Calling API Methods

API endpoints are available as async methods on the client object created above. The calling conventions are given in the Taskcluster reference documentation.

// 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 reference documentation.

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.

Generating 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.

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. If you are not using a credentials agent, but have passed credentials to the client constructor, you can use the synchronous buildSignedUrlSync instead.

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.

Handling Timestamps

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

Generating SlugIDs

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.

Inspecting 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.

Credential Agents

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.

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.


This library is co-versioned with Taskcluster itself. That is, a client with version x.y.z contains API methods corresponding to Taskcluster version x.y.z. Taskcluster is careful to maintain API compatibility, and guarantees it within a major version. That means that any client with version x.* will work against any Taskcluster services at version x.*, and is very likely to work for many other major versions of the Taskcluster services. Any incompatibilities are noted in the Changelog.