New Browser Support Policy

Summary

Establishes a new browser support policy for the next major release of Ember and Ember Data.

Motivation

With Microsoft's recent release of the new Chromium-based Edge browser, which has a compatibility mode for Internet Explorer built in, many frameworks, tools, libraries, and websites have begun finally dropping support for the aging browser. In order to unlock the latest browser features and continue improving the framework as a whole, Ember should also drop support in the next major release.

In dropping support for Internet Explorer, we will need a new browser support policy. Until now Internet Explorer has been the "lowest common denominator" for all features. It is a very old browser that no longer releases new versions, and was not "evergreen" (e.g. constantly updating) even when it was. As such, Ember has been very stable from release to release, as supporting any version of Internet Explorer meant we simply could not use any new browser features.

With modern evergreen browser release cycles, where browsers release regularly and users are generally on one of the more recent versions of a browser, this dynamic changes. We cannot set an explicit version to support anymore, because it would be impractical - Chrome alone releases a new version every 6 weeks. Setting an explicit lowest-supported-version would lock us into having to support a huge number of older browsers, many of which are entirely unused.

Conversely, however, tracking the latest release of a browser may not be enough stability for Ember apps. If Ember were to adopt a new browser feature immediately after its release, even though many web users were still using a previous version, it would cause many Ember apps to either break, or be unable to update until their users had also updated to the latest browser. Even a rolling N - 1 or N - 2 support policy, where the last 1 or 2 versions are supported, may not be enough. Many users were stuck in the recent Edgium update for some time, for instance.

This RFC seeks to establish a new support policy that addresses these issues with a new set of heuristics. These heuristics distinguish between two types of browsers which are supported:

• Evergreen browsers, those which have adopted a continuous update policy and generally keep their users up-to-date automatically.
• Non-evergreen browsers, which have more complicated support patterns that may prevent users from updating regularly.

Depending on which category a browser falls into, different rules will be applied. This will allow us to effectively support browsers which release frequently, such as Chrome, and browsers which do not, such as Safari.

Proposed policy

In the new support policy, Ember will support the following browsers:

• Desktop

1. Google Chrome
2. Mozilla Firefox
3. Microsoft Edge
4. Safari

• Mobile

1. Google Chrome
2. Mozilla Firefox
3. Safari

• Testing

1. Headless Chrome
2. Headless Firefox

Any browser which is not listed here may work, but is not explicitly supported.

In addition, these browsers have been categorized into evergreen and non-evergreen browsers, which have different support policies. This categories have been chose arbitrarily, based on the current state of browsers and their support policies.

• Evergreen

• Desktop

  1. Google Chrome
  2. Chromium
  3. Mozilla Firefox
  4. Microsoft Edge

• Mobile

  1. Google Chrome
  2. Mozilla Firefox

• Testing

  1. Headless Chrome
  2. Headless Firefox

• Non-evergreen

• Desktop

  1. Safari

• Mobile

  1. Safari

This categorization will not change without an additional RFC, even if the browsers themselves make significant changes to their own release process or support system.

Heuristics for browser categorization

As mentioned above, the evergreen and non-evergreen categorization is ultimately arbitrary. However, there were some heuristics which were used to categorize the supported browsers at the time this RFC was made:

1. Evergreen browsers are browsers that:

• Support using the latest version on all supported platforms (e.g. you can use the latest Chrome an any supported version of Windows, macOS, Android, etc. The browser is versioned independently from the operating system).
• Automatically update whenever a new version is available.

1. Non-evergreen browsers are any browsers which do not meet the criteria of evergreen browsers. For instance, Safari is a supported browser whose version is tied to the version of macOS and iOS that users use. As users will often wait to update their operating system, many users lag behind on the version of Safari they are using, so it cannot be considered evergreen.

Evergreen browsers

For a given Ember and Ember Data minor release, the minimum major version supported for a given browser is determined using the following formula.

• Whichever browser version is greater/more recent out of:

1. The lowest/least recent version that fulfills any one of these properties
   • It is the latest version of the browser.
   • It is the latest LTS/extended support version of the browser (such as Firefox ESR).
   • It has at least 0.25% of global marketshare usage across mobile and desktop, based on statcounter.
2. The minimum version supported in the previous release

Within a major version of a browser, the latest patch release is the only release that is supported.

This policy has the following attributes:

• It allows us to generally support the most recent browser versions, which are typically used for some time before everyone upgrades
• It allows us to support browser versions that become temporary "speedbumps" that take longer for users to update, such as the last non-Chromium version of MS Edge.
• It prevents backsliding, once a version is no longer supported, it never becomes supported again.

Above all else, this policy is easy to communicate - for every minor release, we calculate the minimum supported version, and then communicate that we support all versions >= that version.

It is important to note that this policy means that each minor release may drop support for some major versions of evergreen browsers.

Non-evergreen browsers

Ember and Ember Data will support all major versions greater than or equal to the following version for non-evergreen browsers:

• Desktop
• Safari: 12
• Mobile
• Safari: 12

These versions will continue to be supported until support is explicitly dropped via a new RFC, and dropping support for any version of these browsers will require a new major release.

Within a major version of a browser, the latest patch release is the only release that is supported.

Note on the versions chosen

iOS Safari 12 has a usage of ~1.5% globally as of the writing of this RFC. Given this, and the fact that newer versions of Safari do not introduce any major features, 12 seems like an acceptable cutoff at this time.

What support means

This policy governs two major aspects of Ember and Ember Data:

1. When the framework adopts new browser features
2. How the framework responds to bug reports

Ember and Ember Data may introduce new browser feature usage in any minor version release of Ember, provided the feature is supported in all browsers that are supported in this policy at the time the the version in released.

Ember and Ember Data may introduce new browser feature usage in any patch version release of Ember, provided the feature is supported in all browsers that were supported in this policy at the time the minor that the patch is applied to was released. In other words, no breakage can or should occur due to new browser feature usage in any patch release, and if it does, it is a bug.

For bug reports, support is determined by combining our existing Ember version support policy with the browser versions that were supported at the time an Ember version was released. This means Ember will work as time and resourcing is available to fix any browser specific issues that occur in:

1. The current stable and LTS releases of Ember and Ember Data
2. For browsers that were supported by those versions when they were relased

For the previous LTS release, only security bugfixes will be supported, following the existing LTS policy.

Future changes to the policy

This policy is not meant to be immutable. Over time, new browsers could be added to the support matrix, and explicit exceptions could be added for "critical internet infrastructure".

For example, it was well known that Google's search crawler used a very old version of Google Chrome for a very long time. It no longer does and is regularly updated, but during that time frame it was important to support that version of Chrome. Likewise, it was very important to support IE11 for a very long time since it had a large usage percentage, especially in corporate environments. While none of these cases are known to exist at the time of this writing, if one should arise it may be added explicitly via RFC.

Future RFCs may amend this policy in a strictly additive way without requiring a major version bump in Ember. Newly supported browsers will begin being supported in the next minor version of Ember after the updated support policy is implemented.

Future RFCs that amend this policy to remove support for a browser will require a major version of Ember to implement.

Impact on SemVer

While this policy does result in us dropping support for versions of browsers with each minor release, this RFC proposes that this should not have an impact on our SemVer policy. SemVer is a communication mechanism, which is used to communicate to users when impactful changes occur, and what those changes are in broad categories: breaking, new features, bugfixes.

While dropping support for an evergreen browser version could be considered breaking in the strictest technical sense, it generally is not considered one because of the usage patterns that these browsers have in the first place. Their users are automatically opted into updating every time they boot the browser, which means in almost all cases users update quickly and efficiently. In fact, it is often considered a security issue if users are not using the most recent version of an evergreen browser.

As such, the fact is that in most cases, if a bug is somehow reported on an older version of an unsupported browser, then the fix is usually to tell the user to update the browser version, not to patch the application or framework for that browser version. In practice, this is how Ember has operated for years, and this policy only formalizes this process.

Implementation

In order to support this policy while keeping all of our tooling on the same page, Ember.js itself will add automation to calculate the current minimum supported version of browsers on its main branch, and publish them in an accessible format. Each time we branch a release, these versions will stop updating, so they will effectively be locked in.

These versions will be used for a variety of use cases, such as generating documentation and release blog posts (see below), and generating the default config/targets.js for new Ember apps and addons.

Deprecation

We will add a deprecation to Ember CLI that shows when users have any unsupported browser in there targets.json, along with a guide for updating to modern targets.

Implementation timeline

This policy drops support for a major browser, and therefore can only be implemented with a major version bump.

How we teach this

This will be an ongoing process, since the minimum browser versions supported change over time. The most important thing here is that users can easily determine whether or not a given version of a browser is supported for a given Ember release.

The following are the ways we will communicate this:

• For the release blog post for a minor version, we'll include a table which has the list of every supported browser, along with the minimum supported major version of that browser for the release. We will also include the underlying engine version.
• On the releases page of the Ember.js website, for each of the listed releases, we will include a table of the supported versions major browsers for that release.
• The browser support on the releases page for the Stable and LTS branches will be linked in the Ember.js README.

This documentation will be supported by the minimum supported versions that are published in the Ember.js package (see above), which will allow them to be mostly automated. The supported browser table could look like the following (generated using today's usage stats):

Supported Browsers

Desktop

Chrome	Edge	Firefox	Safari
83	18	78 (ESR)	12

Mobile

Chrome	Firefox	Safari
87	83	12

Headless

Chrome	Firefox
87	78 (ESR)

"How we determine support" page

In addition, the technical details of the support policy should be documented on the Ember website, in a less prominent position (e.g. a link from the supported versions table titled "how do we determine browser support?"). This could use the following text:

Ember supports the following major browsers:

• Desktop

1. Google Chrome
2. Mozilla Firefox
3. Microsoft Edge
4. Safari

• Mobile

1. Google Chrome
2. Mozilla Firefox
3. Safari

• Testing

1. Headless Chrome
2. Headless Firefox

Other browsers may work with Ember.js, but are not explicitly supported. If you would like to add support for a new browser, please submit an RFC or RFC issue for discussion!

We determine support on a browser-by-browser basis. Browsers are categorized as either evergreen or non-evergreen. The categorization is as follows:

• Evergreen

• Desktop

  1. Google Chrome
  2. Chromium
  3. Mozilla Firefox
  4. Microsoft Edge

• Mobile

  1. Google Chrome
  2. Mozilla Firefox

• Testing

  1. Headless Chrome
  2. Headless Firefox

• Non-evergreen

• Desktop

  1. Safari

• Mobile

  1. Safari

For evergreen browsers, the minimum version of the browser that we support is determined at the time of every minor release, following this formula:

• Whichever browser version is greater/more recent out of:

1. The lowest/least recent version that fulfills any one of these properties
   • It is the latest version of the browser.
   • It is the latest LTS/extended support version of the browser (such as Firefox ESR).
   • It has at least 0.25% of global marketshare usage across mobile and desktop, based on statcounter.
2. The minimum version supported in the previous release

To simplify, the supported version either moves forward or stays the same for each release based on overall usage and LTS/current release versions.

For non-evergreen browsers, support is locked at a specific major version, and we support all major versions above that version:

• Desktop
• Safari: 12
• Mobile
• Safari: 12

Within a version of a browser, we only support the most recent patch release.

Drawbacks

• The proposed policy makes Safari the new "lowest common denominator" browser, replacing IE11. Since the supported versions of Safari will continue to be supported indefinitely, we will not be able to use any new browser features added afterwards without another major version. In particular, the spec for WeakRef has finally been stabilized, and this is something we'll likely want to make use of in the not-to-distant future.

  While this is true, it does not impact the immediate roadmap for Ember in the next few years. When the time comes, we can update our browser support policy again, and release a new major version.

Alternatives

• Keep things as they are.
• Document the existing policy but do not change it.
• Support fewer browsers, for a shorter amount of time.
• Support more browsers, for a longer amount of time.
• Drop IE11 but not add more definition to support (keeping it as a case by case determination by the core teams)