Announcing Dojo 5.0.0

Dojo version 5 has arrived!

We’re excited to announce the 5.0.0 release of Dojo. This version builds on previous releases with a vast array of bug fixes and improvements throughout the framework.

Conditional Polyfills - Serving Less JavaScript

One of our primary goals for modern Dojo is to improve performance by serving minimal JavaScript bundles by default. For version 5, we’re happy to announce an out of the box solution to optimize the user experience for dealing with bundling and loading polyfills in Dojo applications.

The Dojo build produces separate platform bundles that will be only be loaded based on two key conditions:

1) The shim module is imported somewhere in an application.
1) A users browser does not natively support the browser feature.

In short, if your application does not use the browser feature or you use a browser with native support, the polyfill will not be loaded! This change means serving less JavaScript and improving your application performance without compromising on features.

New Polyfills Added to Shim

We’ve added additional third party polyfills to @dojo/framework/shim:

  • @dojo/framework/shim/fetch - The Fetch API provides an interface for fetching resources (including across the network).
  • @dojo/framework/shim/IntersectionObserver - The Intersection Observer API provides a way to asynchronously observe changes in the intersection of a target element with an ancestor element or with a top-level document’s viewport.
  • @dojo/framework/shim/WebAnimations - The Web Animations API allows for synchronizing and timing changes to the presentation of a Web page, i.e. animation of DOM elements.
  • @dojo/framework/shim/ResizeObserver - The ResizeObserver interface reports changes to the content rectangle of an Element or the bounding box of an SVGElement. The content rectangle is the box in which content can be placed, meaning the border box minus the padding.

To use these additional polyfills they should be imported like any other ponyfill provided by @dojo/framework/shim and they no longer need to be explicitly added/imported to your Dojo application.

Better Build Time Rendering (BTR)

Build time rendering provides the rendering of your application to HTML during the build and in-lines critical CSS. BTR allows an application to render static HTML pages and offer some advantages of server-side rendering (SSR) such as performance and search engine optimization without the complexities of running a server to support full SSR. Build time rendering has been available via the Dojo cli-build-app command since our initial 2.0.0 release.

There are a number of stability and feature enhancements in the 5.0.0 release thanks to the BTR process now running your application in a real browser environment. New features include:

  • Dojo Blocks
  • Support for StateHistory API (see below)
  • Multiple page HTML generation
  • Screenshots of pages visited during Build Time Rendering
  • Better error messaging

Routing support has been extended to support a HistoryManager using the browser history API via the @dojo/framework/routing/history/StateHistory. For StateHistory BTR produces a static HTML file for each of the paths defined in the build time rendering configuration.

To configure build time rendering to create static pages for the BTR paths, ensure you are using the StateHistory in your application and update your BTR config to specify paths without a # prefix.

"build-app": {
    "build-time-render": {
        "root": "app",
        "paths": [

Introducing Dojo Blocks

Dojo Blocks is a new mechanism leveraging Build Time Rendering that allows executing code in Node.js as part of the build. The results from the execution are written to a cache that can then be transparently used in the same way at runtime in the browser. This opens up new opportunities for performing operations that might be not possible or unperformant in a browser.

For example, a Dojo Block module could read a group of markdown files, transform them into VNodes, and make them available to render in the application, all at build time. The result of this Dojo Block module is then cached into the application bundle for use at runtime in the browser.

A Dojo Block module gets used like any other meta in any Dojo widget. As a result there is no extensive configuration or alternative authoring patterns needed.

For example, a block module could read a text file and return the content to the application:

// src/read-file.block.ts
import * as fs from 'fs';
import { resolve } from 'path';

export default (path: string) => {
    path = resolve(__dirname, path);
    return fs.readFileSync(path, 'utf8');

Using the text.block.ts module in your application with the Block meta:

// src/MyBlockWidget.ts
import Block from '@dojo/framework/widget-core/meta/Block';
import WidgetBase from '@dojo/framework/widget-core/WidgetBase';
import { v } from '@dojo/framework/widget-core/d';

import readFile from './read-file.block';

export default class MyBlockWidget extends WidgetBase {
    protected render() {
        const message = this.meta(Block).run(readFile)('../content/hello-dojo-blocks.txt');
        return v('div', [ message ]);

This widget runs the read-file.block.ts module at build time, loading the file path passed which gets used as the children in the widget. The rendered application’s HTML and CSS get written to the built index.html:

    <title>Dojo Blocks</title>
    <meta name="theme-color" content="#222127">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <div id="root"><div>Hello Dojo Block World!</div></div>
    <script type="text/javascript" src="bootstrap.js"></script></body>

Simplifying Testing with Assertion Templates

Assertion Templates make testing widgets with the testing harness even easier. Instead of needing to manually curate each expectedRender result per test, you can now use the Assertion Template primitive to easily modify and layer outputs for the expected render.

Assertion Templates allow you to build expected render functions to pass to h.expect(). Assertion Templates always assert against the entire render output, modifying portions of the assertion itself as needed.

To use Assertion Templates, first import the module:

import assertionTemplate from '@dojo/framework/testing/assertionTemplate';

In your tests, you can then write a base assertion which would be the default render state of your widget.

Given the following widget:

class NumberWidget extends WidgetBase<{ num?: number }> {
    protected render() {
        const { num } =;
        const message = num === undefined ? 'no number passed' : `the number ${num}`;
        return v('div', [
            v('span', [ message ])

The base assertion might look like:

const baseAssertion = assertionTemplate(() => {
    return v('div', [
        v('span', { '~key': 'message' }, [ 'no number passed' ]);

and in a test would look like:

it('should render no number passed when no number is passed as a property', () => {
    const h = harness(() => w(NumberWidget, {}));

Now let’s see how we would test the output when the num property gets passed to the NumberWidget:

it('should render the number when a number is passed as a property', () => {
    const numberAssertion = baseAssertion.setChildren('~message', [ 'the number 5' ]);
    const h = harness(() => w(NumberWidget, { num: 5 }));

Here we’re using the setChildren() API on the baseAssertion, and we’re using a special ~ selector to find a node with a key of ~message. The ~key property is a special property on Assertion Templates and will get erased at assertion time, so it doesn’t show up when matching the renders. This approach allows you to decorate the Assertion Templates to easily select nodes, without having to augment the actual widgets render function.

Once we have the message node we then set the children to the expected the number 5, and use the resulting template in h.expect. It’s important to note Assertion Templates always return a new Assertion Template when setting a value, this ensures you don’t accidentally mutate an existing template (potentially causing other tests to fail), and allows you to compose layered Templates incrementally building on each other.

Improved Stores Middleware

Middleware for Dojo stores has always gotten executed after a process has completed or throws an error, enabling users to make decisions based on the result and perform some additional actions. However, this was limiting middleware from running before or effectively wrapping a process. Version 5 of Dojo introduces before and after middleware to perform such actions around processes completely. Read more on the @dojo/framework/stores readme.

This addition of before and after middleware is a breaking change. However, if your application was already using createCallbackDecorator to create your middleware, then your application should continue to work with your application in version 5 of Dojo application as the createCallbackDecorator function has been adapted to transform existing middleware API to the new API.

Improvements for serve and watch options in @dojo/cli-build-app

The @dojo/cli-build-app command includes a number improvements for running a development server:

  • The previous watch modes, memory and file have been consolidated into a unified watch option
  • Rebuilds your application when you make any changes within the project directory, not limited to src and test directories.
  • Live reload when the application is rebuilt during watch and running the development server using serve
  • Customized live reload client that does not affect your built application bundles
  • Conditionally loads the live reload client only when using the serve option
  • Fallback to default index.html and rewrite resources when using the StateHistory history manager with @dojo/framework/routing

Extended TypeScript Support

Dojo now supports TypeScript versions from 2.6.x to 3.2.x, please see our TypeScript and Dojo compatibility matrix for more information.

Update to Dojo 5.0.0

Visit the Dojo version 5 migration guide for detailed information and guidance on updating your application. Updgrading from 4.0.x to 5.0.0 should require running one command for most users.

After installing the latest version of the @dojo/cli-upgrade-app, run the following command:

dojo upgrade app

Beyond version 5

We are working on a detailed roadmap for the next major release, however, in the meantime check out our future roadmap for ideas we want to investigate over the next 12 months.


See the release notes for more details on version 5 of Dojo.

Love what we’re doing or having a problem? We ❤️ our community. Reach out to us on Discord, check out our roadmap and see where we are heading with Dojo,, and try out the new Dojo on CodeSandbox. We look forward to your feedback.