diff --git a/src/builtin/filters/array.ts b/src/builtin/filters/array.ts
index a56da41df..885e2345a 100644
--- a/src/builtin/filters/array.ts
+++ b/src/builtin/filters/array.ts
@@ -23,7 +23,7 @@ function concat<T1, T2> (v: T1[], arg: T2[] | T2): (T1 | T2)[] {
   return Array.prototype.concat.call(v, arg)
 }
 
-function slice<T> (v: T[], begin: number, length: number = 1): T[] {
+function slice<T> (v: T[], begin: number, length = 1): T[] {
   begin = begin < 0 ? v.length + begin : begin
   return v.slice(begin, begin + length)
 }
diff --git a/src/builtin/filters/math.ts b/src/builtin/filters/math.ts
index 4dc69f84c..3e2b0781a 100644
--- a/src/builtin/filters/math.ts
+++ b/src/builtin/filters/math.ts
@@ -9,7 +9,7 @@ export default {
   'floor': (v: number) => Math.floor(v),
   'minus': (v: number, arg: number) => v - arg,
   'modulo': (v: number, arg: number) => v % arg,
-  'round': (v: number, arg: number = 0) => {
+  'round': (v: number, arg = 0) => {
     const amp = Math.pow(10, arg)
     return Math.round(v * amp) / amp
   },
diff --git a/src/builtin/filters/string.ts b/src/builtin/filters/string.ts
index c09208979..6d82fec7c 100644
--- a/src/builtin/filters/string.ts
+++ b/src/builtin/filters/string.ts
@@ -37,13 +37,13 @@ function replaceFirst (v: string, arg1: string, arg2: string) {
   return stringify(v).replace(arg1, arg2)
 }
 
-function truncate (v: string, l: number = 50, o: string = '...') {
+function truncate (v: string, l = 50, o = '...') {
   v = stringify(v)
   if (v.length <= l) return v
   return v.substr(0, l - o.length) + o
 }
 
-function truncateWords (v: string, l: number = 15, o: string = '...') {
+function truncateWords (v: string, l = 15, o = '...') {
   const arr = v.split(/\s+/)
   let ret = arr.slice(0, l).join(' ')
   if (arr.length >= l) ret += o
diff --git a/src/builtin/tags/raw.ts b/src/builtin/tags/raw.ts
index dd43fd0fe..406edcf05 100644
--- a/src/builtin/tags/raw.ts
+++ b/src/builtin/tags/raw.ts
@@ -1,4 +1,4 @@
-import { TagToken, Token, ITagImplOptions, Context, Emitter, Hash } from '../../types'
+import { TagToken, Token, ITagImplOptions, Context } from '../../types'
 
 export default {
   parse: function (tagToken: TagToken, remainTokens: Token[]) {
diff --git a/src/context/context.ts b/src/context/context.ts
index 5f770e6d5..dddbb996e 100644
--- a/src/context/context.ts
+++ b/src/context/context.ts
@@ -11,7 +11,7 @@ export class Context {
   public environments: Scope
   public sync: boolean
   public opts: NormalizedFullOptions
-  public constructor (ctx: object = {}, opts?: NormalizedFullOptions, sync: boolean = false) {
+  public constructor (ctx: object = {}, opts?: NormalizedFullOptions, sync = false) {
     this.sync = sync
     this.opts = applyDefault(opts)
     this.environments = ctx
diff --git a/src/drop/forloop-drop.ts b/src/drop/forloop-drop.ts
index f902a5663..c076a0e5b 100644
--- a/src/drop/forloop-drop.ts
+++ b/src/drop/forloop-drop.ts
@@ -1,7 +1,7 @@
 import { Drop } from './drop'
 
 export class ForloopDrop extends Drop {
-  protected i: number = 0
+  protected i = 0
   public length: number
   public constructor (length: number) {
     super()
diff --git a/src/liquid.ts b/src/liquid.ts
index 4b881d7ba..d3fe96c3f 100644
--- a/src/liquid.ts
+++ b/src/liquid.ts
@@ -144,4 +144,4 @@ export class Liquid {
     }
     return this.setCache(filepath, tpl)
   }
-}
\ No newline at end of file
+}
diff --git a/src/parser/parse-stream.ts b/src/parser/parse-stream.ts
index ad77fd865..5c4f8e4fd 100644
--- a/src/parser/parse-stream.ts
+++ b/src/parser/parse-stream.ts
@@ -7,7 +7,7 @@ type ParseToken = ((token: Token, remainTokens: Token[]) => ITemplate)
 export class ParseStream {
   private tokens: Token[]
   private handlers: {[key: string]: (arg: any) => void} = {}
-  private stopRequested: boolean = false
+  private stopRequested = false
   private parseToken: ParseToken
 
   public constructor (tokens: Token[], parseToken: ParseToken) {
diff --git a/src/parser/token.ts b/src/parser/token.ts
index 1da596824..162f83426 100644
--- a/src/parser/token.ts
+++ b/src/parser/token.ts
@@ -1,7 +1,7 @@
 export class Token {
-  public trimLeft: boolean = false
-  public trimRight: boolean = false
-  public type: string = 'notset'
+  public trimLeft = false
+  public trimRight = false
+  public type = 'notset'
   public line: number
   public col: number
   public raw: string
diff --git a/src/util/underscore.ts b/src/util/underscore.ts
index 76b2cc34e..90335df42 100644
--- a/src/util/underscore.ts
+++ b/src/util/underscore.ts
@@ -92,7 +92,7 @@ export function isObject (value: any): value is object {
   return value !== null && (type === 'object' || type === 'function')
 }
 
-export function range (start: number, stop: number, step: number = 1) {
+export function range (start: number, stop: number, step = 1) {
   const arr: number[] = []
   for (let i = start; i < stop; i += step) {
     arr.push(i)
@@ -100,7 +100,7 @@ export function range (start: number, stop: number, step: number = 1) {
   return arr
 }
 
-export function padStart (str: any, length: number, ch: string = ' ') {
+export function padStart (str: any, length: number, ch = ' ') {
   str = String(str)
   let n = length - str.length
   while (n-- > 0) str = ch + str
diff --git a/test/e2e/drop.ts b/test/e2e/drop.ts
index c4a3a1cfa..3edd0db06 100644
--- a/test/e2e/drop.ts
+++ b/test/e2e/drop.ts
@@ -5,7 +5,7 @@ import * as chaiAsPromised from 'chai-as-promised'
 use(chaiAsPromised)
 
 class SettingsDrop extends Drop {
-  private foo: string = 'FOO'
+  private foo = 'FOO'
   public bar () {
     return 'BAR'
   }
diff --git a/test/integration/drop/drop.ts b/test/integration/drop/drop.ts
index bd81ba21b..656ed709c 100644
--- a/test/integration/drop/drop.ts
+++ b/test/integration/drop/drop.ts
@@ -6,7 +6,7 @@ describe('drop/drop', function () {
   before(() => (liquid = new Liquid()))
 
   class CustomDrop extends Drop {
-    private name: string = 'NAME'
+    private name = 'NAME'
     public getName () {
       return 'GET NAME'
     }