Ember 2 To 3 Migration

Ember 2.18 → 3.28 LTS Migration

The fastest, safest path from Ember 2.x is to walk the LTS chain. Each LTS is a stable target; each hop fixes the deprecations the next hop expects to be gone.

2.18 LTS  ─┐
           ├→  3.4 LTS   ─┐
                          ├→  3.8 LTS  ─┐
                                        ├→  3.12 LTS  ─┐
                                                       ├→  3.16 LTS  ─┐
                                                                      ├→  3.20 LTS  ─┐
                                                                                     ├→  3.24 LTS  ─┐
                                                                                                    ├→  3.28 LTS
                                                                                                       (last 3.x)

You do not jump directly. The shortest path that works in practice is 2.18 → 3.4 → 3.8 → 3.12 → 3.16 → 3.20 → 3.24 → 3.28. Each hop is one or two days of work for a typical mid-size app; it can be many weeks for a 2014-era monolith.

Once at 3.28, hand off to the ember-3-migrator agent (and the ember-3-octane-adoption / ember-3-to-4-migration skills) to plan 3 → 4.

Tool of record: ember-cli-update

ember-cli-update regenerates the project files for a target Ember/CLI version, then asks you to merge the diff. It's the single best leverage point in the upgrade.

# install once
pnpm add -D ember-cli-update

# bump to a target version
pnpm exec ember-cli-update --to 3.4

# resolve the conflicts it surfaces, then:
pnpm exec ember-cli-update --run-codemods

Codemods you'll meet:

Codemods are helpers, not magic. Always review the diff and run tests.

The deprecation workflow — the actual loop

The repeated pattern at every hop:

1. Update ember-source, ember-cli, ember-data to the next LTS.
2. Boot the app, watch the console.
3. For every deprecation message:
     a. Find the offending line via the stack.
     b. Either fix it or stash it via ember-cli-deprecation-workflow.
4. Run the test suite. Fix breakage.
5. Smoke-test the top user flows manually.
6. Commit per-deprecation when reasonable, so the diff is reviewable.
7. Move to the next LTS.

Use ember-cli-deprecation-workflow to silence deprecations you don't have time to fix yet:

// config/deprecation-workflow.js
self.deprecationWorkflow = self.deprecationWorkflow || {};
self.deprecationWorkflow.config = {
  workflow: [
    { handler: 'silence', matchId: 'ember-component.send-action' },
    { handler: 'silence', matchId: 'ember-views.curly-components.jquery-element' }
  ]
};

This unblocks the hop without committing to fixing every deprecation in the same week. Track silenced deprecations in an issue and burn them down later.

Hop-by-hop guide

2.18 → 3.4

This is the deepest hop because it crosses the major version line. The rest are easier.

What changes:

• Ember.X global access starts emitting deprecations everywhere → run ember-modules-codemod.
• ember-cli configuration changes (ember-cli-build.js shape, addon hooks).
• Bower is dropped — anything you load via bower.json must move to npm.
• ember-data 3.x requires explicit relationship inverses to be set if you customize them.
• The 2.x test API still works, but ember-qunit@^4 adds the new style alongside.

What to watch:

• jQuery is still bundled. You'll see the deprecation about Ember.$ and this.$(), but it's not removed yet.
• Closure actions ((action "save" post)) replace sendAction everywhere.

3.4 → 3.8

• componentName.toString() deprecations.
• More _super chain warnings.
• Stricter RouterDSL (e.g. nested route paths must not start with /).

3.8 → 3.12

• Octane appears in the air: @glimmer/component, @tracked, modifiers, native classes, decorators are all stable but optional. Don't adopt yet — finish the deprecation pass first.
• jQuery becomes optional (@ember/optional-features). You can disable it now — many tests will need updating from this.$() to find().

pnpm exec ember feature:disable jquery-integration

3.12 → 3.16

• Ember.run namespace deprecations: rename to @ember/runloop imports.
• Deprecations around Ember.String extensions ('foo'.camelize() etc.) — import explicitly from @ember/string.
• Glimmer 2 compilation pipeline becomes the default. Some HTMLBars-only tricks stop working.

3.16 → 3.20

• Many more "Octane mental model" hints in the console. Still optional, but the runway is shrinking.
• ember-cli reaches a build pipeline that handles ES modules cleanly — many addon issues evaporate at this point.

3.20 → 3.24

• Component naming becomes stricter (the resolver expects file paths to match invocation names).
• tagless components emit clearer deprecations.

3.24 → 3.28

The final 3.x. 3.28 LTS is the canonical "stop here, take stock, plan the 4.x jump" station.

What to do at 3.28:

• All Ember.* global access is gone (or silenced).
• Tests are mostly modernized (module + setupApplicationTest + await).
• Octane is opted-in via config/optional-features.json:

  {
    "application-template-wrapper": false,
    "default-async-observers": true,
    "jquery-integration": false,
    "template-only-glimmer-components": true
  }
  

• Components have been selectively ported to @glimmer/component — usually the leaf components first.
• The deprecation workflow file should be empty or near-empty.

This is a great moment to add CI gates: error on new deprecations, fail on new Ember.* imports, lint rules against extend()-style classes.

jQuery removal — usually the longest pole

jQuery removal cuts across templates, components, and tests. A practical order:

1. Tests first. Replace this.$(...) with find(...), findAll(...), assert.dom(...). Smaller blast radius.
2. Component DOM hooks. didInsertElement(){ this.$('.x').focus(); } → modifier ({{auto-focus}}).
3. AJAX. Ember.$.ajax(...) → fetch or ember-fetch. Keep response shape identical to avoid serializer changes.
4. Plugins. Any "wrap a jQuery plugin" pattern → custom modifier with proper teardown.

Disable the integration with ember feature:disable jquery-integration only after the four steps above are done. If you turn it off prematurely, every render will break loudly.

Ember Data hop

ember-data 2.x → 3.x → 3.28 is a parallel track:

• DS.Model.extend({...}) still works in 3.x but begins emitting deprecations late in 3.x.
• Implicit relationship inverses become explicit-required. Fix @belongsTo/@hasMany to specify inverse: 'fieldName' at every site.
• import DS from 'ember-data' is gradually replaced by import Model, { attr, belongsTo, hasMany } from '@ember-data/model'.
• The RESTSerializer/JSONAPISerializer defaults stayed stable; don't rewrite them mid-migration.

Addon survival list

Common 2.x addons and their fate:

Run pnpm exec ember-cli-update --addons (in newer versions of the tool) to surface addons that block the bump.

Tests — the safety net throughout

Before each hop:

1. Run the full suite — baseline green.
2. Bump.
3. Run the full suite — fix until green again.
4. Manually smoke-test the top user flows. Tests don't catch everything; in 2.x they often miss a lot.

If your suite is thin, the first investment is more tests, not the upgrade. Migrating a flaky test suite is worse than not migrating.

Time estimates (rough, mid-size app)

Add a multiplier for:

• Heavy classic-component DOM manipulation.
• Many archived addons (each one needs an own decision).
• Thin tests (you'll be hand-verifying flows).

Verification — at the 3.28 finish line

• ember-source is ~3.28.x.
• ember-cli-update reports no pending diffs for 3.28.
• All Ember.X direct imports have been replaced or silenced.
• jquery-integration optional feature is false.
• Tests run on the modern API (module + setupApplicationTest); andThen is gone.
• ember-cli-deprecation-workflow.js is empty or has only well-known, owner-assigned silences.
• Octane optional features are enabled in config/optional-features.json.
• Addons are upgraded to versions that work on 3.28.
• pnpm test is green; CI is green.

When the box is fully checked, switch to the ember-3-to-4-migration skill.

See also

• ember-2-recommendations — surviving while you plan.
• ember-3-to-4-migration — the next hop.
• Official: emberjs.com/releases, Deprecations app, ember-cli-update.