diff --git a/.eslintrc.js b/.eslintrc.js
index 98303eb24..8ea5865e8 100644
--- a/.eslintrc.js
+++ b/.eslintrc.js
@@ -45,6 +45,7 @@ module.exports = {
     'array-callback-return': 'error',
     'callback-return': 'error',
     'global-require': 'error',
+    'guard-for-in': 'error',
     /* End v2 rules */
     'arrow-parens': 'error',
     'no-tabs': 'error',
diff --git a/app/scripts/controllers/preferences.js b/app/scripts/controllers/preferences.js
index 855a07c0c..47fa73746 100644
--- a/app/scripts/controllers/preferences.js
+++ b/app/scripts/controllers/preferences.js
@@ -337,9 +337,9 @@ export default class PreferencesController {
       }
 
       // store lost accounts
-      for (const key in newlyLost) {
+      Object.keys(newlyLost).forEach((key) => {
         lostIdentities[key] = newlyLost[key]
-      }
+      })
     }
 
     this.store.updateState({ identities, lostIdentities })
diff --git a/app/scripts/lib/ComposableObservableStore.js b/app/scripts/lib/ComposableObservableStore.js
index d8308465b..3f8b99af4 100644
--- a/app/scripts/lib/ComposableObservableStore.js
+++ b/app/scripts/lib/ComposableObservableStore.js
@@ -25,9 +25,11 @@ export default class ComposableObservableStore extends ObservableStore {
     this.config = config
     this.removeAllListeners()
     for (const key in config) {
-      config[key].subscribe((state) => {
-        this.updateState({ [key]: state })
-      })
+      if (config.hasOwnProperty(key)) {
+        config[key].subscribe((state) => {
+          this.updateState({ [key]: state })
+        })
+      }
     }
   }
 
@@ -40,9 +42,11 @@ export default class ComposableObservableStore extends ObservableStore {
   getFlatState () {
     let flatState = {}
     for (const key in this.config) {
-      const controller = this.config[key]
-      const state = controller.getState ? controller.getState() : controller.state
-      flatState = { ...flatState, ...state }
+      if (this.config.hasOwnProperty(key)) {
+        const controller = this.config[key]
+        const state = controller.getState ? controller.getState() : controller.state
+        flatState = { ...flatState, ...state }
+      }
     }
     return flatState
   }
diff --git a/app/scripts/lib/migrator/index.js b/app/scripts/lib/migrator/index.js
index ebc70f73f..a82b93294 100644
--- a/app/scripts/lib/migrator/index.js
+++ b/app/scripts/lib/migrator/index.js
@@ -35,8 +35,7 @@ export default class Migrator extends EventEmitter {
     const pendingMigrations = this.migrations.filter(migrationIsPending)
 
     // perform each migration
-    for (const index in pendingMigrations) {
-      const migration = pendingMigrations[index]
+    for (const migration of pendingMigrations) {
       try {
         // attempt migration and validate
         const migratedData = await migration.migrate(versionedData)
diff --git a/app/scripts/migrations/028.js b/app/scripts/migrations/028.js
index 583f3299d..09fc18f11 100644
--- a/app/scripts/migrations/028.js
+++ b/app/scripts/migrations/028.js
@@ -29,9 +29,9 @@ function transformState (state) {
       const identities = newState.PreferencesController.identities
       const tokens = newState.PreferencesController.tokens
       newState.PreferencesController.accountTokens = {}
-      for (const identity in identities) {
+      Object.keys(identities).forEach((identity) => {
         newState.PreferencesController.accountTokens[identity] = { 'mainnet': tokens }
-      }
+      })
       newState.PreferencesController.tokens = []
     }
   }
diff --git a/app/scripts/migrations/037.js b/app/scripts/migrations/037.js
index 42287af4f..1d7f13810 100644
--- a/app/scripts/migrations/037.js
+++ b/app/scripts/migrations/037.js
@@ -27,9 +27,9 @@ function transformState (state) {
     const newAddressBook = {}
 
     // add all of the chainIds to a set
-    for (const item in ab) {
-      chainIds.add(ab[item].chainId)
-    }
+    Object.values(ab).forEach((v) => {
+      chainIds.add(v.chainId)
+    })
 
     // fill the chainId object with the entries with the matching chainId
     for (const id of chainIds.values()) {
diff --git a/test/unit/app/controllers/transactions/tx-state-manager-test.js b/test/unit/app/controllers/transactions/tx-state-manager-test.js
index 5290bbd81..abd7a7098 100644
--- a/test/unit/app/controllers/transactions/tx-state-manager-test.js
+++ b/test/unit/app/controllers/transactions/tx-state-manager-test.js
@@ -323,7 +323,7 @@ describe('TransactionStateManager', function () {
       }
       const invalidValues = [1, true, {}, Symbol('1')]
 
-      for (const key in validTxParams) {
+      Object.keys(validTxParams).forEach((key) => {
         for (const value of invalidValues) {
           const tx = {
             id: 1,
@@ -339,7 +339,7 @@ describe('TransactionStateManager', function () {
           assert.ok(Array.isArray(result), 'txList should be an array')
           assert.equal(result.length, 0, 'txList should be empty')
         }
-      }
+      })
     })
 
     it('does not override txs from other networks', function () {
@@ -416,7 +416,7 @@ describe('TransactionStateManager', function () {
 
       txStateManager.addTx({ id: 1, status: 'unapproved', metamaskNetworkId: currentNetworkId, txParams: validTxParams })
 
-      for (const key in validTxParams) {
+      Object.keys(validTxParams).forEach((key) => {
         for (const value of invalidValues) {
           const originalTx = txStateManager.getTx(1)
           const newTx = {
@@ -430,7 +430,7 @@ describe('TransactionStateManager', function () {
           const result = txStateManager.getTx(1)
           assert.deepEqual(result, originalTx, 'tx should not be updated')
         }
-      }
+      })
     })
 
     it('updates gas price and adds history items', function () {
diff --git a/ui/app/components/app/modals/fade-modal.js b/ui/app/components/app/modals/fade-modal.js
index 873861e27..a59c8995b 100644
--- a/ui/app/components/app/modals/fade-modal.js
+++ b/ui/app/components/app/modals/fade-modal.js
@@ -25,16 +25,16 @@ const insertKeyframesRule = (keyframes) => {
   const name = 'anim_' + (++index) + (+new Date())
   let css = '@' + 'keyframes ' + name + ' {'
 
-  for (const key in keyframes) {
+  Object.keys(keyframes).forEach((key) => {
     css += key + ' {'
 
-    for (const property in keyframes[key]) {
+    Object.keys(keyframes[key]).forEach((property) => {
       const part = ':' + keyframes[key][property] + ';'
       css += property + part
-    }
+    })
 
     css += '}'
-  }
+  })
 
   css += '}'
 
diff --git a/ui/app/helpers/utils/util.js b/ui/app/helpers/utils/util.js
index 37f852530..7643519a8 100644
--- a/ui/app/helpers/utils/util.js
+++ b/ui/app/helpers/utils/util.js
@@ -28,9 +28,9 @@ const valueTable = {
   tether: '0.000000000001',
 }
 const bnTable = {}
-for (const currency in valueTable) {
+Object.keys(valueTable).forEach((currency) => {
   bnTable[currency] = new ethUtil.BN(valueTable[currency], 10)
-}
+})
 
 export function isEthNetwork (netId) {
   if (!netId || netId === '1' || netId === '3' || netId === '4' || netId === '42' || netId === '5777') {
diff --git a/ui/app/helpers/utils/util.test.js b/ui/app/helpers/utils/util.test.js
index 4be1713e9..ef1f5f153 100644
--- a/ui/app/helpers/utils/util.test.js
+++ b/ui/app/helpers/utils/util.test.js
@@ -230,11 +230,11 @@ describe('util', function () {
         }
         const oneEthBn = new ethUtil.BN(ethInWei, 10)
 
-        for (const currency in valueTable) {
+        Object.keys(valueTable).forEach((currency) => {
           const value = new ethUtil.BN(valueTable[currency], 10)
           const output = util.normalizeToWei(value, currency)
           assert.equal(output.toString(10), valueTable.wei, `value of ${output.toString(10)} ${currency} should convert to ${oneEthBn}`)
-        }
+        })
       })
     })