diff --git a/packages/reactivity/src/computed.ts b/packages/reactivity/src/computed.ts
index 3bb3c3e2..c22a33e4 100644
--- a/packages/reactivity/src/computed.ts
+++ b/packages/reactivity/src/computed.ts
@@ -33,8 +33,8 @@ export function computed<T>(
       }
     : (getterOrOptions as WritableComputedOptions<T>).set
 
-  let dirty: boolean = true
-  let value: any = undefined
+  let dirty = true
+  let value: T
 
   const runner = effect(getter, {
     lazy: true,
diff --git a/packages/reactivity/src/effect.ts b/packages/reactivity/src/effect.ts
index a147e613..a542e3b6 100644
--- a/packages/reactivity/src/effect.ts
+++ b/packages/reactivity/src/effect.ts
@@ -160,8 +160,8 @@ export function trigger(
     // never been tracked
     return
   }
-  const effects: Set<ReactiveEffect> = new Set()
-  const computedRunners: Set<ReactiveEffect> = new Set()
+  const effects = new Set<ReactiveEffect>()
+  const computedRunners = new Set<ReactiveEffect>()
   if (type === OperationTypes.CLEAR) {
     // collection being cleared, trigger all effects for target
     depsMap.forEach(dep => {
diff --git a/packages/reactivity/src/reactive.ts b/packages/reactivity/src/reactive.ts
index 28c74720..b703154e 100644
--- a/packages/reactivity/src/reactive.ts
+++ b/packages/reactivity/src/reactive.ts
@@ -15,20 +15,20 @@ import { ReactiveEffect } from './effect'
 // raw Sets to reduce memory overhead.
 export type Dep = Set<ReactiveEffect>
 export type KeyToDepMap = Map<string | symbol, Dep>
-export const targetMap: WeakMap<any, KeyToDepMap> = new WeakMap()
+export const targetMap = new WeakMap<any, KeyToDepMap>()
 
 // WeakMaps that store {raw <-> observed} pairs.
-const rawToReactive: WeakMap<any, any> = new WeakMap()
-const reactiveToRaw: WeakMap<any, any> = new WeakMap()
-const rawToReadonly: WeakMap<any, any> = new WeakMap()
-const readonlyToRaw: WeakMap<any, any> = new WeakMap()
+const rawToReactive = new WeakMap<any, any>()
+const reactiveToRaw = new WeakMap<any, any>()
+const rawToReadonly = new WeakMap<any, any>()
+const readonlyToRaw = new WeakMap<any, any>()
 
 // WeakSets for values that are marked readonly or non-reactive during
 // observable creation.
-const readonlyValues: WeakSet<any> = new WeakSet()
-const nonReactiveValues: WeakSet<any> = new WeakSet()
+const readonlyValues = new WeakSet<any>()
+const nonReactiveValues = new WeakSet<any>()
 
-const collectionTypes: Set<any> = new Set([Set, Map, WeakMap, WeakSet])
+const collectionTypes = new Set<Function>([Set, Map, WeakMap, WeakSet])
 const observableValueRE = /^\[object (?:Object|Array|Map|Set|WeakMap|WeakSet)\]$/
 
 const canObserve = (value: any): boolean => {