diff --git a/jest.config.js b/jest.config.js
index 7f426e738..4eb301058 100644
--- a/jest.config.js
+++ b/jest.config.js
@@ -1,5 +1,9 @@
 module.exports = {
   preset: 'ts-jest',
+  globals: {
+    __DEV__: true,
+    __COMPAT__: false
+  },
   coverageDirectory: 'coverage',
   coverageReporters: ['html', 'lcov', 'text'],
   collectCoverageFrom: ['packages/*/src/**/*.ts'],
diff --git a/package.json b/package.json
index 2de822a58..ba43dde54 100644
--- a/package.json
+++ b/package.json
@@ -6,7 +6,7 @@
   "scripts": {
     "dev": "node scripts/dev.js",
     "build": "node scripts/build.js",
-    "lint": "prettier --write --parser typescript 'packages/*/src/**/*.ts'"
+    "lint": "prettier --write --parser typescript 'packages/**/*.ts'"
   },
   "gitHooks": {
     "pre-commit": "lint-staged",
diff --git a/packages/observer/README.md b/packages/observer/README.md
index 0fd7a6c50..db173a913 100644
--- a/packages/observer/README.md
+++ b/packages/observer/README.md
@@ -1,3 +1,13 @@
 # @vue/observer
 
-> This package is inlined into Global & Browser ESM builds of user-facing renderers (e.g. `@vue/renderer-dom`), but also published as a package that can be used standalone. The standalone build should not be used alongside a pre-bundled build of a user-facing renderer, as they will have different internal storage for reactivity connections. A user-facing renderer should re-export all APIs from this package.
+## Usage Note
+
+This package is inlined into Global & Browser ESM builds of user-facing renderers (e.g. `@vue/renderer-dom`), but also published as a package that can be used standalone. The standalone build should not be used alongside a pre-bundled build of a user-facing renderer, as they will have different internal storage for reactivity connections. A user-facing renderer should re-export all APIs from this package.
+
+## Credits
+
+The implementation of this module is inspired by the following prior art in the JavaScript ecosystem:
+
+- [Meteor Tracker](https://docs.meteor.com/api/tracker.html)
+- [nx-js/observer-util](https://github.com/nx-js/observer-util)
+- [salesforce/observable-membrane](https://github.com/salesforce/observable-membrane)
diff --git a/packages/observer/__tests__/autorun.spec.ts b/packages/observer/__tests__/autorun.spec.ts
new file mode 100644
index 000000000..c0c8c4739
--- /dev/null
+++ b/packages/observer/__tests__/autorun.spec.ts
@@ -0,0 +1,642 @@
+import {
+  observable,
+  autorun,
+  stop,
+  unwrap,
+  OperationTypes,
+  DebuggerEvent,
+  markNonReactive
+} from '../src/index'
+import { ITERATE_KEY } from '../src/autorun'
+
+describe('observer/autorun', () => {
+  it('should run the passed function once (wrapped by a autorun)', () => {
+    const fnSpy = jest.fn(() => {})
+    autorun(fnSpy)
+    expect(fnSpy).toHaveBeenCalledTimes(1)
+  })
+
+  it('should observe basic properties', () => {
+    let dummy
+    const counter = observable({ num: 0 })
+    autorun(() => (dummy = counter.num))
+
+    expect(dummy).toBe(0)
+    counter.num = 7
+    expect(dummy).toBe(7)
+  })
+
+  it('should observe multiple properties', () => {
+    let dummy
+    const counter = observable({ num1: 0, num2: 0 })
+    autorun(() => (dummy = counter.num1 + counter.num1 + counter.num2))
+
+    expect(dummy).toBe(0)
+    counter.num1 = counter.num2 = 7
+    expect(dummy).toBe(21)
+  })
+
+  it('should handle multiple autoruns', () => {
+    let dummy1, dummy2
+    const counter = observable({ num: 0 })
+    autorun(() => (dummy1 = counter.num))
+    autorun(() => (dummy2 = counter.num))
+
+    expect(dummy1).toBe(0)
+    expect(dummy2).toBe(0)
+    counter.num++
+    expect(dummy1).toBe(1)
+    expect(dummy2).toBe(1)
+  })
+
+  it('should observe nested properties', () => {
+    let dummy
+    const counter = observable({ nested: { num: 0 } })
+    autorun(() => (dummy = counter.nested.num))
+
+    expect(dummy).toBe(0)
+    counter.nested.num = 8
+    expect(dummy).toBe(8)
+  })
+
+  it('should observe delete operations', () => {
+    let dummy
+    const obj = observable({ prop: 'value' })
+    autorun(() => (dummy = obj.prop))
+
+    expect(dummy).toBe('value')
+    delete obj.prop
+    expect(dummy).toBe(undefined)
+  })
+
+  it('should observe has operations', () => {
+    let dummy
+    const obj: any = observable({ prop: 'value' })
+    autorun(() => (dummy = 'prop' in obj))
+
+    expect(dummy).toBe(true)
+    delete obj.prop
+    expect(dummy).toBe(false)
+    obj.prop = 12
+    expect(dummy).toBe(true)
+  })
+
+  it('should observe properties on the prototype chain', () => {
+    let dummy
+    const counter = observable({ num: 0 })
+    const parentCounter = observable({ num: 2 })
+    Object.setPrototypeOf(counter, parentCounter)
+    autorun(() => (dummy = counter.num))
+
+    expect(dummy).toBe(0)
+    delete counter.num
+    expect(dummy).toBe(2)
+    parentCounter.num = 4
+    expect(dummy).toBe(4)
+    counter.num = 3
+    expect(dummy).toBe(3)
+  })
+
+  it('should observe has operations on the prototype chain', () => {
+    let dummy
+    const counter = observable({ num: 0 })
+    const parentCounter = observable({ num: 2 })
+    Object.setPrototypeOf(counter, parentCounter)
+    autorun(() => (dummy = 'num' in counter))
+
+    expect(dummy).toBe(true)
+    delete counter.num
+    expect(dummy).toBe(true)
+    delete parentCounter.num
+    expect(dummy).toBe(false)
+    counter.num = 3
+    expect(dummy).toBe(true)
+  })
+
+  it('should observe inherited property accessors', () => {
+    let dummy, parentDummy, hiddenValue: any
+    const obj: any = observable({})
+    const parent = observable({
+      set prop(value) {
+        hiddenValue = value
+      },
+      get prop() {
+        return hiddenValue
+      }
+    })
+    Object.setPrototypeOf(obj, parent)
+    autorun(() => (dummy = obj.prop))
+    autorun(() => (parentDummy = parent.prop))
+
+    expect(dummy).toBe(undefined)
+    expect(parentDummy).toBe(undefined)
+    obj.prop = 4
+    expect(dummy).toBe(4)
+    // this doesn't work, should it?
+    // expect(parentDummy).toBe(4)
+    parent.prop = 2
+    expect(dummy).toBe(2)
+    expect(parentDummy).toBe(2)
+  })
+
+  it('should observe function call chains', () => {
+    let dummy
+    const counter = observable({ num: 0 })
+    autorun(() => (dummy = getNum()))
+
+    function getNum() {
+      return counter.num
+    }
+
+    expect(dummy).toBe(0)
+    counter.num = 2
+    expect(dummy).toBe(2)
+  })
+
+  it('should observe iteration', () => {
+    let dummy
+    const list = observable(['Hello'])
+    autorun(() => (dummy = list.join(' ')))
+
+    expect(dummy).toBe('Hello')
+    list.push('World!')
+    expect(dummy).toBe('Hello World!')
+    list.shift()
+    expect(dummy).toBe('World!')
+  })
+
+  it('should observe implicit array length changes', () => {
+    let dummy
+    const list = observable(['Hello'])
+    autorun(() => (dummy = list.join(' ')))
+
+    expect(dummy).toBe('Hello')
+    list[1] = 'World!'
+    expect(dummy).toBe('Hello World!')
+    list[3] = 'Hello!'
+    expect(dummy).toBe('Hello World!  Hello!')
+  })
+
+  it('should observe sparse array mutations', () => {
+    let dummy
+    const list: any[] = observable([])
+    list[1] = 'World!'
+    autorun(() => (dummy = list.join(' ')))
+
+    expect(dummy).toBe(' World!')
+    list[0] = 'Hello'
+    expect(dummy).toBe('Hello World!')
+    list.pop()
+    expect(dummy).toBe('Hello')
+  })
+
+  it('should observe enumeration', () => {
+    let dummy = 0
+    const numbers: any = observable({ num1: 3 })
+    autorun(() => {
+      dummy = 0
+      for (let key in numbers) {
+        dummy += numbers[key]
+      }
+    })
+
+    expect(dummy).toBe(3)
+    numbers.num2 = 4
+    expect(dummy).toBe(7)
+    delete numbers.num1
+    expect(dummy).toBe(4)
+  })
+
+  it('should observe symbol keyed properties', () => {
+    const key = Symbol('symbol keyed prop')
+    let dummy, hasDummy
+    const obj = observable({ [key]: 'value' })
+    autorun(() => (dummy = obj[key]))
+    autorun(() => (hasDummy = key in obj))
+
+    expect(dummy).toBe('value')
+    expect(hasDummy).toBe(true)
+    obj[key] = 'newValue'
+    expect(dummy).toBe('newValue')
+    delete obj[key]
+    expect(dummy).toBe(undefined)
+    expect(hasDummy).toBe(false)
+  })
+
+  it('should not observe well-known symbol keyed properties', () => {
+    const key = Symbol.isConcatSpreadable
+    let dummy
+    const array: any = observable([])
+    autorun(() => (dummy = array[key]))
+
+    expect(array[key]).toBe(undefined)
+    expect(dummy).toBe(undefined)
+    array[key] = true
+    expect(array[key]).toBe(true)
+    expect(dummy).toBe(undefined)
+  })
+
+  it('should observe function valued properties', () => {
+    const oldFunc = () => {}
+    const newFunc = () => {}
+
+    let dummy
+    const obj = observable({ func: oldFunc })
+    autorun(() => (dummy = obj.func))
+
+    expect(dummy).toBe(oldFunc)
+    obj.func = newFunc
+    expect(dummy).toBe(newFunc)
+  })
+
+  it('should not observe set operations without a value change', () => {
+    let hasDummy, getDummy
+    const obj = observable({ prop: 'value' })
+
+    const getSpy = jest.fn(() => (getDummy = obj.prop))
+    const hasSpy = jest.fn(() => (hasDummy = 'prop' in obj))
+    autorun(getSpy)
+    autorun(hasSpy)
+
+    expect(getDummy).toBe('value')
+    expect(hasDummy).toBe(true)
+    obj.prop = 'value'
+    expect(getSpy).toHaveBeenCalledTimes(1)
+    expect(hasSpy).toHaveBeenCalledTimes(1)
+    expect(getDummy).toBe('value')
+    expect(hasDummy).toBe(true)
+  })
+
+  it('should not observe raw mutations', () => {
+    let dummy
+    const obj: any = observable()
+    autorun(() => (dummy = unwrap(obj).prop))
+
+    expect(dummy).toBe(undefined)
+    obj.prop = 'value'
+    expect(dummy).toBe(undefined)
+  })
+
+  it('should not be triggered by raw mutations', () => {
+    let dummy
+    const obj: any = observable()
+    autorun(() => (dummy = obj.prop))
+
+    expect(dummy).toBe(undefined)
+    unwrap(obj).prop = 'value'
+    expect(dummy).toBe(undefined)
+  })
+
+  it('should not be triggered by inherited raw setters', () => {
+    let dummy, parentDummy, hiddenValue: any
+    const obj: any = observable({})
+    const parent = observable({
+      set prop(value) {
+        hiddenValue = value
+      },
+      get prop() {
+        return hiddenValue
+      }
+    })
+    Object.setPrototypeOf(obj, parent)
+    autorun(() => (dummy = obj.prop))
+    autorun(() => (parentDummy = parent.prop))
+
+    expect(dummy).toBe(undefined)
+    expect(parentDummy).toBe(undefined)
+    unwrap(obj).prop = 4
+    expect(dummy).toBe(undefined)
+    expect(parentDummy).toBe(undefined)
+  })
+
+  it('should avoid implicit infinite recursive loops with itself', () => {
+    const counter = observable({ num: 0 })
+
+    const counterSpy = jest.fn(() => counter.num++)
+    autorun(counterSpy)
+    expect(counter.num).toBe(1)
+    expect(counterSpy).toHaveBeenCalledTimes(1)
+    counter.num = 4
+    expect(counter.num).toBe(5)
+    expect(counterSpy).toHaveBeenCalledTimes(2)
+  })
+
+  it('should allow explicitly recursive raw function loops', () => {
+    const counter = observable({ num: 0 })
+
+    // TODO: this should be changed to autorun loops, can it be done?
+    const numSpy = jest.fn(() => {
+      counter.num++
+      if (counter.num < 10) {
+        numSpy()
+      }
+    })
+    autorun(numSpy)
+
+    expect(counter.num).toEqual(10)
+    expect(numSpy).toHaveBeenCalledTimes(10)
+  })
+
+  it('should avoid infinite loops with other autoruns', () => {
+    const nums = observable({ num1: 0, num2: 1 })
+
+    const spy1 = jest.fn(() => (nums.num1 = nums.num2))
+    const spy2 = jest.fn(() => (nums.num2 = nums.num1))
+    autorun(spy1)
+    autorun(spy2)
+    expect(nums.num1).toBe(1)
+    expect(nums.num2).toBe(1)
+    expect(spy1).toHaveBeenCalledTimes(1)
+    expect(spy2).toHaveBeenCalledTimes(1)
+    nums.num2 = 4
+    expect(nums.num1).toBe(4)
+    expect(nums.num2).toBe(4)
+    expect(spy1).toHaveBeenCalledTimes(2)
+    expect(spy2).toHaveBeenCalledTimes(2)
+    nums.num1 = 10
+    expect(nums.num1).toBe(10)
+    expect(nums.num2).toBe(10)
+    expect(spy1).toHaveBeenCalledTimes(3)
+    expect(spy2).toHaveBeenCalledTimes(3)
+  })
+
+  it('should return a new reactive version of the function', () => {
+    function greet() {
+      return 'Hello World'
+    }
+    const autorun1 = autorun(greet)
+    const autorun2 = autorun(greet)
+    expect(typeof autorun1).toBe('function')
+    expect(typeof autorun2).toBe('function')
+    expect(autorun1).not.toBe(greet)
+    expect(autorun1).not.toBe(autorun2)
+  })
+
+  it('should discover new branches while running automatically', () => {
+    let dummy
+    const obj = observable({ prop: 'value', run: false })
+
+    const conditionalSpy = jest.fn(() => {
+      dummy = obj.run ? obj.prop : 'other'
+    })
+    autorun(conditionalSpy)
+
+    expect(dummy).toBe('other')
+    expect(conditionalSpy).toHaveBeenCalledTimes(1)
+    obj.prop = 'Hi'
+    expect(dummy).toBe('other')
+    expect(conditionalSpy).toHaveBeenCalledTimes(1)
+    obj.run = true
+    expect(dummy).toBe('Hi')
+    expect(conditionalSpy).toHaveBeenCalledTimes(2)
+    obj.prop = 'World'
+    expect(dummy).toBe('World')
+    expect(conditionalSpy).toHaveBeenCalledTimes(3)
+  })
+
+  it('should discover new branches when running manually', () => {
+    let dummy
+    let run = false
+    const obj = observable({ prop: 'value' })
+    const runner = autorun(() => {
+      dummy = run ? obj.prop : 'other'
+    })
+
+    expect(dummy).toBe('other')
+    runner()
+    expect(dummy).toBe('other')
+    run = true
+    runner()
+    expect(dummy).toBe('value')
+    obj.prop = 'World'
+    expect(dummy).toBe('World')
+  })
+
+  it('should not be triggered by mutating a property, which is used in an inactive branch', () => {
+    let dummy
+    const obj = observable({ prop: 'value', run: true })
+
+    const conditionalSpy = jest.fn(() => {
+      dummy = obj.run ? obj.prop : 'other'
+    })
+    autorun(conditionalSpy)
+
+    expect(dummy).toBe('value')
+    expect(conditionalSpy).toHaveBeenCalledTimes(1)
+    obj.run = false
+    expect(dummy).toBe('other')
+    expect(conditionalSpy).toHaveBeenCalledTimes(2)
+    obj.prop = 'value2'
+    expect(dummy).toBe('other')
+    expect(conditionalSpy).toHaveBeenCalledTimes(2)
+  })
+
+  it('should not double wrap if the passed function is a autorun', () => {
+    const runner = autorun(() => {})
+    const otherRunner = autorun(runner)
+    expect(runner).not.toBe(otherRunner)
+    expect(runner.raw).toBe(otherRunner.raw)
+  })
+
+  it('should not run multiple times for a single mutation', () => {
+    let dummy
+    const obj: any = observable()
+    const fnSpy = jest.fn(() => {
+      for (const key in obj) {
+        dummy = obj[key]
+      }
+      dummy = obj.prop
+    })
+    autorun(fnSpy)
+
+    expect(fnSpy).toHaveBeenCalledTimes(1)
+    obj.prop = 16
+    expect(dummy).toBe(16)
+    expect(fnSpy).toHaveBeenCalledTimes(2)
+  })
+
+  it('should allow nested autoruns', () => {
+    const nums = observable({ num1: 0, num2: 1, num3: 2 })
+    const dummy: any = {}
+
+    const childSpy = jest.fn(() => (dummy.num1 = nums.num1))
+    const childautorun = autorun(childSpy)
+    const parentSpy = jest.fn(() => {
+      dummy.num2 = nums.num2
+      childautorun()
+      dummy.num3 = nums.num3
+    })
+    autorun(parentSpy)
+
+    expect(dummy).toEqual({ num1: 0, num2: 1, num3: 2 })
+    expect(parentSpy).toHaveBeenCalledTimes(1)
+    expect(childSpy).toHaveBeenCalledTimes(2)
+    // this should only call the childautorun
+    nums.num1 = 4
+    expect(dummy).toEqual({ num1: 4, num2: 1, num3: 2 })
+    expect(parentSpy).toHaveBeenCalledTimes(1)
+    expect(childSpy).toHaveBeenCalledTimes(3)
+    // this calls the parentautorun, which calls the childautorun once
+    nums.num2 = 10
+    expect(dummy).toEqual({ num1: 4, num2: 10, num3: 2 })
+    expect(parentSpy).toHaveBeenCalledTimes(2)
+    expect(childSpy).toHaveBeenCalledTimes(4)
+    // this calls the parentautorun, which calls the childautorun once
+    nums.num3 = 7
+    expect(dummy).toEqual({ num1: 4, num2: 10, num3: 7 })
+    expect(parentSpy).toHaveBeenCalledTimes(3)
+    expect(childSpy).toHaveBeenCalledTimes(5)
+  })
+
+  test('should observe class method invocations', () => {
+    class Model {
+      count: number
+      constructor() {
+        this.count = 0
+      }
+      inc() {
+        this.count++
+      }
+    }
+    const model = observable(new Model())
+    let dummy
+    autorun(() => {
+      dummy = model.count
+    })
+    expect(dummy).toBe(0)
+    model.inc()
+    expect(dummy).toBe(1)
+  })
+
+  test('scheduler', () => {
+    let runner: any, dummy
+    const scheduler = jest.fn(_runner => {
+      runner = _runner
+    })
+    const obj = observable({ foo: 1 })
+    autorun(
+      () => {
+        dummy = obj.foo
+      },
+      { scheduler }
+    )
+    expect(scheduler).not.toHaveBeenCalled()
+    expect(dummy).toBe(1)
+    // should be called on first trigger
+    obj.foo++
+    expect(scheduler).toHaveBeenCalledTimes(1)
+    // should not run yet
+    expect(dummy).toBe(1)
+    // manually run
+    runner()
+    // should have run
+    expect(dummy).toBe(2)
+  })
+
+  test('events: onTrack', () => {
+    let events: any[] = []
+    let dummy
+    const onTrack = jest.fn((e: DebuggerEvent) => {
+      events.push(e)
+    })
+    const obj = observable({ foo: 1, bar: 2 })
+    const runner = autorun(
+      () => {
+        dummy = obj.foo
+        dummy = 'bar' in obj
+        dummy = Object.keys(obj)
+      },
+      { onTrack }
+    )
+    expect(dummy).toEqual(['foo', 'bar'])
+    expect(onTrack).toHaveBeenCalledTimes(3)
+    expect(events).toEqual([
+      {
+        runner,
+        target: unwrap(obj),
+        type: OperationTypes.GET,
+        key: 'foo'
+      },
+      {
+        runner,
+        target: unwrap(obj),
+        type: OperationTypes.HAS,
+        key: 'bar'
+      },
+      {
+        runner,
+        target: unwrap(obj),
+        type: OperationTypes.ITERATE,
+        key: ITERATE_KEY
+      }
+    ])
+  })
+
+  test('events: onTrigger', () => {
+    let events: any[] = []
+    let dummy
+    const onTrigger = jest.fn((e: DebuggerEvent) => {
+      events.push(e)
+    })
+    const obj = observable({ foo: 1 })
+    const runner = autorun(
+      () => {
+        dummy = obj.foo
+      },
+      { onTrigger }
+    )
+
+    obj.foo++
+    expect(dummy).toBe(2)
+    expect(onTrigger).toHaveBeenCalledTimes(1)
+    expect(events[0]).toEqual({
+      runner,
+      target: unwrap(obj),
+      type: OperationTypes.SET,
+      key: 'foo',
+      oldValue: 1,
+      newValue: 2
+    })
+
+    delete obj.foo
+    expect(dummy).toBeUndefined()
+    expect(onTrigger).toHaveBeenCalledTimes(2)
+    expect(events[1]).toEqual({
+      runner,
+      target: unwrap(obj),
+      type: OperationTypes.DELETE,
+      key: 'foo',
+      oldValue: 2
+    })
+  })
+
+  test('stop', () => {
+    let dummy
+    const obj = observable({ prop: 1 })
+    const runner = autorun(() => {
+      dummy = obj.prop
+    })
+    obj.prop = 2
+    expect(dummy).toBe(2)
+    stop(runner)
+    obj.prop = 3
+    expect(dummy).toBe(2)
+  })
+
+  test('markNonReactive', () => {
+    const obj = observable({
+      foo: markNonReactive({
+        prop: 0
+      })
+    })
+    let dummy
+    autorun(() => {
+      dummy = obj.foo.prop
+    })
+    expect(dummy).toBe(0)
+    obj.foo.prop++
+    expect(dummy).toBe(0)
+    obj.foo = { prop: 1 }
+    expect(dummy).toBe(1)
+  })
+})
diff --git a/packages/observer/__tests__/collections.spec.ts b/packages/observer/__tests__/collections.spec.ts
new file mode 100644
index 000000000..da242d716
--- /dev/null
+++ b/packages/observer/__tests__/collections.spec.ts
@@ -0,0 +1 @@
+describe('observer/collections', () => {})
diff --git a/packages/observer/__tests__/computed.spec.ts b/packages/observer/__tests__/computed.spec.ts
new file mode 100644
index 000000000..04114631d
--- /dev/null
+++ b/packages/observer/__tests__/computed.spec.ts
@@ -0,0 +1 @@
+describe('observer/computed', () => {})
diff --git a/packages/observer/__tests__/immutable.spec.ts b/packages/observer/__tests__/immutable.spec.ts
new file mode 100644
index 000000000..64d6e2aa5
--- /dev/null
+++ b/packages/observer/__tests__/immutable.spec.ts
@@ -0,0 +1 @@
+describe('observer/immutable', () => {})
diff --git a/packages/observer/__tests__/observable.spec.ts b/packages/observer/__tests__/observable.spec.ts
new file mode 100644
index 000000000..86792c2b4
--- /dev/null
+++ b/packages/observer/__tests__/observable.spec.ts
@@ -0,0 +1,154 @@
+import { observable, isObservable, unwrap, markNonReactive } from '../src/index'
+
+describe('observer/observable', () => {
+  test('Object', () => {
+    const original = { foo: 1 }
+    const observed = observable(original)
+    expect(observed).not.toBe(original)
+    expect(isObservable(observed)).toBe(true)
+    expect(isObservable(original)).toBe(false)
+    // get
+    expect(observed.foo).toBe(1)
+    // has
+    expect('foo' in observed).toBe(true)
+    // ownKeys
+    expect(Object.keys(observed)).toEqual(['foo'])
+  })
+
+  test('Array', () => {
+    const original: any[] = [{ foo: 1 }]
+    const observed = observable(original)
+    expect(observed).not.toBe(original)
+    expect(isObservable(observed)).toBe(true)
+    expect(isObservable(original)).toBe(false)
+    expect(isObservable(observed[0])).toBe(true)
+    // get
+    expect(observed[0].foo).toBe(1)
+    // has
+    expect(0 in observed).toBe(true)
+    // ownKeys
+    expect(Object.keys(observed)).toEqual(['0'])
+  })
+
+  test('cloned observable Array should point to observed values', () => {
+    const original = [{ foo: 1 }]
+    const observed = observable(original)
+    const clone = observed.slice()
+    expect(isObservable(clone[0])).toBe(true)
+    expect(clone[0]).not.toBe(original[0])
+    expect(clone[0]).toBe(observed[0])
+  })
+
+  test('nested observables', () => {
+    const original = {
+      nested: {
+        foo: 1
+      },
+      array: [{ bar: 2 }]
+    }
+    const observed = observable(original)
+    expect(isObservable(observed.nested)).toBe(true)
+    expect(isObservable(observed.array)).toBe(true)
+    expect(isObservable(observed.array[0])).toBe(true)
+  })
+
+  test('observed value should proxy mutations to original (Object)', () => {
+    const original: any = { foo: 1 }
+    const observed = observable(original)
+    // set
+    observed.bar = 1
+    expect(observed.bar).toBe(1)
+    expect(original.bar).toBe(1)
+    // delete
+    delete observed.foo
+    expect('foo' in observed).toBe(false)
+    expect('foo' in original).toBe(false)
+  })
+
+  test('observed value should proxy mutations to original (Array)', () => {
+    const original: any[] = [{ foo: 1 }, { bar: 2 }]
+    const observed = observable(original)
+    // set
+    const value = { baz: 3 }
+    const observableValue = observable(value)
+    observed[0] = value
+    expect(observed[0]).toBe(observableValue)
+    expect(original[0]).toBe(value)
+    // delete
+    delete observed[0]
+    expect(observed[0]).toBeUndefined()
+    expect(original[0]).toBeUndefined()
+    // mutating methods
+    observed.push(value)
+    expect(observed[2]).toBe(observableValue)
+    expect(original[2]).toBe(value)
+  })
+
+  test('setting a property with an unobserved value should wrap with observable', () => {
+    const observed: any = observable({})
+    const raw = {}
+    observed.foo = raw
+    expect(observed.foo).not.toBe(raw)
+    expect(isObservable(observed.foo)).toBe(true)
+  })
+
+  test('observing already observed value should return same Proxy', () => {
+    const original = { foo: 1 }
+    const observed = observable(original)
+    const observed2 = observable(observed)
+    expect(observed2).toBe(observed)
+  })
+
+  test('observing the same value multiple times should return same Proxy', () => {
+    const original = { foo: 1 }
+    const observed = observable(original)
+    const observed2 = observable(original)
+    expect(observed2).toBe(observed)
+  })
+
+  test('should not pollute original object with Proxies', () => {
+    const original: any = { foo: 1 }
+    const original2 = { bar: 2 }
+    const observed = observable(original)
+    const observed2 = observable(original2)
+    observed.bar = observed2
+    expect(observed.bar).toBe(observed2)
+    expect(original.bar).toBe(original2)
+  })
+
+  test('unwrap', () => {
+    const original = { foo: 1 }
+    const observed = observable(original)
+    expect(unwrap(observed)).toBe(original)
+    expect(unwrap(original)).toBe(original)
+  })
+
+  test('unobservable values', () => {
+    const msg = 'not observable'
+    // number
+    expect(() => observable(1)).toThrowError(msg)
+    // string
+    expect(() => observable('foo')).toThrowError(msg)
+    // boolean
+    expect(() => observable(false)).toThrowError(msg)
+    // null
+    expect(() => observable(null)).toThrowError(msg)
+    // undefined should work because it returns empty object observable
+    expect(() => observable(undefined)).not.toThrowError(msg)
+    // symbol
+    const s = Symbol()
+    expect(() => observable(s)).toThrowError(msg)
+    // built-ins should work and return same value
+    const p = Promise.resolve()
+    expect(observable(p)).toBe(p)
+  })
+
+  test('markNonReactive', () => {
+    const obj = observable({
+      foo: { a: 1 },
+      bar: markNonReactive({ b: 2 })
+    })
+    expect(isObservable(obj.foo)).toBe(true)
+    expect(isObservable(obj.bar)).toBe(false)
+  })
+})
diff --git a/packages/observer/src/autorun.ts b/packages/observer/src/autorun.ts
index 6752bf76d..b4a1cb6cb 100644
--- a/packages/observer/src/autorun.ts
+++ b/packages/observer/src/autorun.ts
@@ -32,12 +32,13 @@ export type Debugger = (event: DebuggerEvent) => void
 
 export const activeAutorunStack: Autorun[] = []
 
-const ITERATE_KEY = Symbol('iterate')
+export const ITERATE_KEY = Symbol('iterate')
 
 export function createAutorun(fn: Function, options: AutorunOptions): Autorun {
   const runner = function runner(...args): any {
     return run(runner as Autorun, fn, args)
   } as Autorun
+  runner.isAutorun = true
   runner.active = true
   runner.raw = fn
   runner.scheduler = options.scheduler
diff --git a/packages/observer/src/index.ts b/packages/observer/src/index.ts
index 1aa0c1d1b..379595398 100644
--- a/packages/observer/src/index.ts
+++ b/packages/observer/src/index.ts
@@ -24,6 +24,7 @@ import {
 } from './autorun'
 
 export { Autorun, DebuggerEvent }
+export { OperationTypes } from './operations'
 export { computed, ComputedGetter } from './computed'
 export { lock, unlock } from './lock'
 
@@ -40,7 +41,7 @@ const canObserve = (value: any): boolean => {
   )
 }
 
-type identity = <T>(target: T) => T
+type identity = <T>(target?: T) => T
 
 export const observable = ((target: any = {}): any => {
   // if trying to observe an immutable proxy, return the immutable version.
diff --git a/packages/scheduler/__tests__/scheduler.spec.ts b/packages/scheduler/__tests__/scheduler.spec.ts
index 864845e0f..60f4494bf 100644
--- a/packages/scheduler/__tests__/scheduler.spec.ts
+++ b/packages/scheduler/__tests__/scheduler.spec.ts
@@ -1,78 +1,80 @@
 import { queueJob, nextTick } from '../src/index'
 
-test('queueJob', async () => {
-  const calls: any = []
-  const job1 = () => {
-    calls.push('job1')
-  }
-  const job2 = () => {
-    calls.push('job2')
-  }
-  queueJob(job1)
-  queueJob(job2)
-  expect(calls).toEqual([])
-  await nextTick()
-  expect(calls).toEqual(['job1', 'job2'])
-})
-
-test('queueJob while already flushing', async () => {
-  const calls: any = []
-  const job1 = () => {
-    calls.push('job1')
-    // job1 queues job2
+describe('scheduler', () => {
+  test('queueJob', async () => {
+    const calls: any = []
+    const job1 = () => {
+      calls.push('job1')
+    }
+    const job2 = () => {
+      calls.push('job2')
+    }
+    queueJob(job1)
     queueJob(job2)
-    // should be called sync
+    expect(calls).toEqual([])
+    await nextTick()
     expect(calls).toEqual(['job1', 'job2'])
-  }
-  const job2 = () => {
-    calls.push('job2')
-  }
-  queueJob(job1)
-  expect(calls).toEqual([])
-  await nextTick()
-  expect(calls).toEqual(['job1', 'job2'])
-})
+  })
 
-test('queueJob w/ postFlushCb', async () => {
-  const calls: any = []
-  const job1 = () => {
-    calls.push('job1')
-  }
-  const job2 = () => {
-    calls.push('job2')
-  }
-  const cb1 = () => {
-    calls.push('cb1')
-  }
-  const cb2 = () => {
-    calls.push('cb2')
-  }
-  queueJob(job1, cb1)
-  queueJob(job2, cb2)
-  await nextTick()
-  expect(calls).toEqual(['job1', 'job2', 'cb1', 'cb2'])
-})
+  test('queueJob while already flushing', async () => {
+    const calls: any = []
+    const job1 = () => {
+      calls.push('job1')
+      // job1 queues job2
+      queueJob(job2)
+      // should be called sync
+      expect(calls).toEqual(['job1', 'job2'])
+    }
+    const job2 = () => {
+      calls.push('job2')
+    }
+    queueJob(job1)
+    expect(calls).toEqual([])
+    await nextTick()
+    expect(calls).toEqual(['job1', 'job2'])
+  })
 
-test('queueJob w/ postFlushCb while flushing', async () => {
-  const calls: any = []
-  const job1 = () => {
-    calls.push('job1')
-    // job1 queues job2
+  test('queueJob w/ postFlushCb', async () => {
+    const calls: any = []
+    const job1 = () => {
+      calls.push('job1')
+    }
+    const job2 = () => {
+      calls.push('job2')
+    }
+    const cb1 = () => {
+      calls.push('cb1')
+    }
+    const cb2 = () => {
+      calls.push('cb2')
+    }
+    queueJob(job1, cb1)
     queueJob(job2, cb2)
-    // should be called sync
-    expect(calls).toEqual(['job1', 'job2'])
-  }
-  const job2 = () => {
-    calls.push('job2')
-  }
-  const cb1 = () => {
-    calls.push('cb1')
-  }
-  const cb2 = () => {
-    calls.push('cb2')
-  }
-  queueJob(job1, cb1)
-  expect(calls).toEqual([])
-  await nextTick()
-  expect(calls).toEqual(['job1', 'job2', 'cb1', 'cb2'])
+    await nextTick()
+    expect(calls).toEqual(['job1', 'job2', 'cb1', 'cb2'])
+  })
+
+  test('queueJob w/ postFlushCb while flushing', async () => {
+    const calls: any = []
+    const job1 = () => {
+      calls.push('job1')
+      // job1 queues job2
+      queueJob(job2, cb2)
+      // should be called sync
+      expect(calls).toEqual(['job1', 'job2'])
+    }
+    const job2 = () => {
+      calls.push('job2')
+    }
+    const cb1 = () => {
+      calls.push('cb1')
+    }
+    const cb2 = () => {
+      calls.push('cb2')
+    }
+    queueJob(job1, cb1)
+    expect(calls).toEqual([])
+    await nextTick()
+    expect(calls).toEqual(['job1', 'job2', 'cb1', 'cb2'])
+  })
 })