diff --git a/src/builtin/tags/for.ts b/src/builtin/tags/for.ts
index 5d2ce8cd1b..fb7430355f 100644
--- a/src/builtin/tags/for.ts
+++ b/src/builtin/tags/for.ts
@@ -48,7 +48,7 @@ export default <ITagImplOptions>{
       if (isString(collection) && collection.length > 0) {
         collection = [collection] as string[]
       } else if (isObject(collection)) {
-        collection = Object.keys(collection).map((key) => [key, collection[key]]) as Array<[string, any]>
+        collection = Object.keys(collection).map((key) => [key, collection[key]])
       }
     }
     if (!isArray(collection) || !collection.length) {
diff --git a/src/context/context.ts b/src/context/context.ts
index 8a72e5ceb9..eb481085e9 100644
--- a/src/context/context.ts
+++ b/src/context/context.ts
@@ -45,7 +45,7 @@ export default class Context {
     }
     return this.scopes.splice(i, 1)[0]
   }
-  findScope (key: string) {
+  private findScope (key: string) {
     for (let i = this.scopes.length - 1; i >= 0; i--) {
       const candidate = this.scopes[i]
       if (key in candidate) {
@@ -73,7 +73,7 @@ export default class Context {
    * accessSeq("foo['b]r']")      // ['foo', 'b]r']
    * accessSeq("foo[bar.coo]")    // ['foo', 'bar'], for bar.coo == 'bar'
    */
-  async parseProp (str: string) {
+  private async parseProp (str: string) {
     str = String(str)
     const seq: string[] = []
     let name = ''
@@ -107,8 +107,7 @@ export default class Context {
           i++
           break
         default:// foo.bar
-          name += str[i]
-          i++
+          name += str[i++]
       }
     }
     push()
diff --git a/src/parser/delimited-token.ts b/src/parser/delimited-token.ts
index 625fa54bb1..bc3d011b8e 100644
--- a/src/parser/delimited-token.ts
+++ b/src/parser/delimited-token.ts
@@ -2,17 +2,26 @@ import Token from './token'
 import { last } from '../util/underscore'
 
 export default class DelimitedToken extends Token {
-  trimLeft: boolean
-  trimRight: boolean
-  constructor (raw: string, value: string, input: string, line: number, pos: number, file?: string) {
+  constructor (
+    raw: string,
+    value: string,
+    input: string,
+    line: number,
+    pos: number,
+    trimLeft: boolean,
+    trimRight: boolean,
+    file?: string
+  ) {
     super(raw, input, line, pos, file)
-    this.trimLeft = value[0] === '-'
-    this.trimRight = last(value) === '-'
+    const tl = value[0] === '-'
+    const tr = last(value) === '-'
     this.value = value
       .slice(
-        this.trimLeft ? 1 : 0,
-        this.trimRight ? -1 : value.length
+        tl ? 1 : 0,
+        tr ? -1 : value.length
       )
       .trim()
+    this.trimLeft = tl || trimLeft
+    this.trimRight = tr || trimRight
   }
 }
diff --git a/src/parser/html-token.ts b/src/parser/html-token.ts
index 5418388d57..53d70515ab 100644
--- a/src/parser/html-token.ts
+++ b/src/parser/html-token.ts
@@ -6,4 +6,7 @@ export default class HTMLToken extends Token {
     this.type = 'html'
     this.value = str
   }
+  static is (token: Token): token is HTMLToken {
+    return token.type === 'html'
+  }
 }
diff --git a/src/parser/output-token.ts b/src/parser/output-token.ts
index 31b9f7be81..7674729d59 100644
--- a/src/parser/output-token.ts
+++ b/src/parser/output-token.ts
@@ -1,8 +1,21 @@
 import DelimitedToken from './delimited-token'
+import Token from './token'
+import { NormalizedFullOptions } from '../liquid-options'
 
 export default class OutputToken extends DelimitedToken {
-  constructor (raw: string, value: string, input: string, line: number, pos: number, file?: string) {
-    super(raw, value, input, line, pos, file)
+  constructor (
+    raw: string,
+    value: string,
+    input: string,
+    line: number,
+    pos: number,
+    options: NormalizedFullOptions,
+    file?: string
+  ) {
+    super(raw, value, input, line, pos, options.trimOutputLeft, options.trimOutputRight, file)
     this.type = 'output'
   }
+  static is (token: Token): token is OutputToken {
+    return token.type === 'output'
+  }
 }
diff --git a/src/parser/parse-stream.ts b/src/parser/parse-stream.ts
index ea91df55fb..6141e092f6 100644
--- a/src/parser/parse-stream.ts
+++ b/src/parser/parse-stream.ts
@@ -18,20 +18,16 @@ export default class ParseStream {
     this.handlers[name] = cb
     return this
   }
-  trigger <T extends Token | ITemplate> (event: string, arg?: T) {
+  private trigger <T extends Token | ITemplate> (event: string, arg?: T) {
     const h = this.handlers[event]
-    if (typeof h === 'function') {
-      h(arg)
-      return true
-    }
-    return false
+    return h ? (h(arg), true) : false
   }
   start () {
     this.trigger('start')
     let token: Token | undefined
     while (!this.stopRequested && (token = this.tokens.shift())) {
       if (this.trigger('token', token)) continue
-      if (token.type === 'tag' && this.trigger(`tag:${(<TagToken>token).name}`, token)) {
+      if (TagToken.is(token) && this.trigger(`tag:${token.name}`, token)) {
         continue
       }
       const template = this.parseToken(token, this.tokens)
diff --git a/src/parser/parser.ts b/src/parser/parser.ts
index bf1f5fc295..4fead687a3 100644
--- a/src/parser/parser.ts
+++ b/src/parser/parser.ts
@@ -25,10 +25,10 @@ export default class Parser {
   }
   parseToken (token: Token, remainTokens: Array<Token>) {
     try {
-      if (token.type === 'tag') {
-        return new Tag(token as TagToken, remainTokens, this.liquid)
+      if (TagToken.is(token)) {
+        return new Tag(token, remainTokens, this.liquid)
       }
-      if (token.type === 'output') {
+      if (OutputToken.is(token)) {
         return new Output(token as OutputToken, this.liquid.options.strictFilters)
       }
       return new HTML(token)
diff --git a/src/parser/tag-token.ts b/src/parser/tag-token.ts
index a4ebc1d93d..7cec7673ee 100644
--- a/src/parser/tag-token.ts
+++ b/src/parser/tag-token.ts
@@ -1,12 +1,22 @@
 import DelimitedToken from './delimited-token'
+import Token from './token'
 import { TokenizationError } from '../util/error'
 import * as lexical from './lexical'
+import { NormalizedFullOptions } from '../liquid-options'
 
 export default class TagToken extends DelimitedToken {
   name: string
   args: string
-  constructor (raw: string, value: string, input: string, line: number, pos: number, file?: string) {
-    super(raw, value, input, line, pos, file)
+  constructor (
+    raw: string,
+    value: string,
+    input: string,
+    line: number,
+    pos: number,
+    options: NormalizedFullOptions,
+    file?: string
+  ) {
+    super(raw, value, input, line, pos, options.trimTagLeft, options.trimTagRight, file)
     this.type = 'tag'
     const match = this.value.match(lexical.tagLine)
     if (!match) {
@@ -15,4 +25,7 @@ export default class TagToken extends DelimitedToken {
     this.name = match[1]
     this.args = match[2]
   }
+  static is (token: Token): token is TagToken {
+    return token.type === 'tag'
+  }
 }
diff --git a/src/parser/token.ts b/src/parser/token.ts
index a13b539c91..7a493ffc75 100644
--- a/src/parser/token.ts
+++ b/src/parser/token.ts
@@ -1,4 +1,6 @@
 export default class Token {
+  trimLeft: boolean = false
+  trimRight: boolean = false
   type: string = 'notset'
   line: number
   col: number
diff --git a/src/parser/tokenizer.ts b/src/parser/tokenizer.ts
index 02c41414d8..40e7b7c3d5 100644
--- a/src/parser/tokenizer.ts
+++ b/src/parser/tokenizer.ts
@@ -9,16 +9,18 @@ import { NormalizedFullOptions, applyDefault } from '../liquid-options'
 enum ParseState { HTML, OUTPUT, TAG }
 
 export default class Tokenizer {
-  options: NormalizedFullOptions
+  private options: NormalizedFullOptions
   constructor (options?: NormalizedFullOptions) {
     this.options = applyDefault(options)
   }
   tokenize (input: string, file?: string) {
     const tokens: Token[] = []
-    const tagL = this.options.tagDelimiterLeft
-    const tagR = this.options.tagDelimiterRight
-    const outputL = this.options.outputDelimiterLeft
-    const outputR = this.options.outputDelimiterRight
+    const {
+      tagDelimiterLeft,
+      tagDelimiterRight,
+      outputDelimiterLeft,
+      outputDelimiterRight
+    } = this.options
     let p = 0
     let curLine = 1
     let state = ParseState.HTML
@@ -33,36 +35,39 @@ export default class Tokenizer {
         lineBegin = p + 1
       }
       if (state === ParseState.HTML) {
-        if (input.substr(p, outputL.length) === outputL) {
+        if (input.substr(p, outputDelimiterLeft.length) === outputDelimiterLeft) {
           if (buffer) tokens.push(new HTMLToken(buffer, input, line, col, file))
-          buffer = outputL
+          buffer = outputDelimiterLeft
           line = curLine
           col = p - lineBegin + 1
-          p += outputL.length
+          p += outputDelimiterLeft.length
           state = ParseState.OUTPUT
           continue
-        } else if (input.substr(p, tagL.length) === tagL) {
+        } else if (input.substr(p, tagDelimiterLeft.length) === tagDelimiterLeft) {
           if (buffer) tokens.push(new HTMLToken(buffer, input, line, col, file))
-          buffer = tagL
+          buffer = tagDelimiterLeft
           line = curLine
           col = p - lineBegin + 1
-          p += tagL.length
+          p += tagDelimiterLeft.length
           state = ParseState.TAG
           continue
         }
-      } else if (state === ParseState.OUTPUT && input.substr(p, outputR.length) === outputR) {
-        buffer += outputR
-        tokens.push(new OutputToken(buffer, buffer.slice(outputL.length, -outputR.length), input, line, col, file))
-        p += outputR.length
+      } else if (
+        state === ParseState.OUTPUT &&
+        input.substr(p, outputDelimiterRight.length) === outputDelimiterRight
+      ) {
+        buffer += outputDelimiterRight
+        tokens.push(new OutputToken(buffer, buffer.slice(outputDelimiterLeft.length, -outputDelimiterRight.length), input, line, col, this.options, file))
+        p += outputDelimiterRight.length
         buffer = ''
         line = curLine
         col = p - lineBegin + 1
         state = ParseState.HTML
         continue
-      } else if (input.substr(p, tagR.length) === tagR) {
-        buffer += tagR
-        tokens.push(new TagToken(buffer, buffer.slice(tagL.length, -tagR.length), input, line, col, file))
-        p += tagR.length
+      } else if (input.substr(p, tagDelimiterRight.length) === tagDelimiterRight) {
+        buffer += tagDelimiterRight
+        tokens.push(new TagToken(buffer, buffer.slice(tagDelimiterLeft.length, -tagDelimiterRight.length), input, line, col, this.options, file))
+        p += tagDelimiterRight.length
         buffer = ''
         line = curLine
         col = p - lineBegin + 1
diff --git a/src/parser/whitespace-ctrl.ts b/src/parser/whitespace-ctrl.ts
index ce7d8600b9..c66fbe947f 100644
--- a/src/parser/whitespace-ctrl.ts
+++ b/src/parser/whitespace-ctrl.ts
@@ -1,47 +1,38 @@
-import DelimitedToken from '../parser/delimited-token'
 import Token from '../parser/token'
 import TagToken from '../parser/tag-token'
+import HTMLToken from '../parser/html-token'
 import { NormalizedFullOptions } from '../liquid-options'
 
 export default function whiteSpaceCtrl (tokens: Token[], options: NormalizedFullOptions) {
   options = { greedy: true, ...options }
   let inRaw = false
 
-  tokens.forEach((token: Token, i: number) => {
-    if (shouldTrimLeft(token as DelimitedToken, inRaw, options)) {
+  for (let i = 0; i < tokens.length; i++) {
+    const token = tokens[i]
+    if (!inRaw && token.trimLeft) {
       trimLeft(tokens[i - 1], options.greedy)
     }
 
-    if (token.type === 'tag' && (token as TagToken).name === 'raw') inRaw = true
-    if (token.type === 'tag' && (token as TagToken).name === 'endraw') inRaw = false
+    if (TagToken.is(token)) {
+      if (token.name === 'raw') inRaw = true
+      else if (token.name === 'endraw') inRaw = false
+    }
 
-    if (shouldTrimRight(token as DelimitedToken, inRaw, options)) {
+    if (!inRaw && token.trimRight) {
       trimRight(tokens[i + 1], options.greedy)
     }
-  })
-}
-
-function shouldTrimLeft (token: DelimitedToken, inRaw: boolean, options: NormalizedFullOptions) {
-  if (inRaw) return false
-  if (token.type === 'tag') return token.trimLeft || options.trimTagLeft
-  if (token.type === 'output') return token.trimLeft || options.trimOutputLeft
-}
-
-function shouldTrimRight (token: DelimitedToken, inRaw: boolean, options: NormalizedFullOptions) {
-  if (inRaw) return false
-  if (token.type === 'tag') return token.trimRight || options.trimTagRight
-  if (token.type === 'output') return token.trimRight || options.trimOutputRight
+  }
 }
 
 function trimLeft (token: Token, greedy: boolean) {
-  if (!token || token.type !== 'html') return
+  if (!token || !HTMLToken.is(token)) return
 
   const rLeft = greedy ? /\s+$/g : /[\t\r ]*$/g
   token.value = token.value.replace(rLeft, '')
 }
 
 function trimRight (token: Token, greedy: boolean) {
-  if (!token || token.type !== 'html') return
+  if (!token || !HTMLToken.is(token)) return
 
   const rRight = greedy ? /^\s+/g : /^[\t\r ]*\n?/g
   token.value = token.value.replace(rRight, '')
diff --git a/src/render/syntax.ts b/src/render/syntax.ts
index e76594eb97..d694760f6f 100644
--- a/src/render/syntax.ts
+++ b/src/render/syntax.ts
@@ -1,7 +1,7 @@
 import * as lexical from '../parser/lexical'
 import assert from '../util/assert'
 import Context from '../context/context'
-import { range, last } from '../util/underscore'
+import { range, last, isFunction } from '../util/underscore'
 import { isComparable } from '../drop/icomparable'
 import { NullDrop } from '../drop/null-drop'
 import { EmptyDrop } from '../drop/empty-drop'
@@ -40,9 +40,7 @@ const binaryOperators: {[key: string]: (lhs: any, rhs: any) => boolean} = {
     return l <= r
   },
   'contains': (l: any, r: any) => {
-    if (!l) return false
-    if (typeof l.indexOf !== 'function') return false
-    return l.indexOf(r) > -1
+    return l && isFunction(l.indexOf) ? l.indexOf(r) > -1 : false
   },
   'and': (l: any, r: any) => isTruthy(l) && isTruthy(r),
   'or': (l: any, r: any) => isTruthy(l) || isTruthy(r)
diff --git a/src/template/tag/tag.ts b/src/template/tag/tag.ts
index e91744729b..91366153f0 100644
--- a/src/template/tag/tag.ts
+++ b/src/template/tag/tag.ts
@@ -1,4 +1,4 @@
-import { create, stringify } from '../../util/underscore'
+import { stringify, isFunction } from '../../util/underscore'
 import assert from '../../util/assert'
 import Context from '../../context/context'
 import ITagImpl from './itag-impl'
@@ -21,7 +21,8 @@ export default class Tag extends Template<TagToken> implements ITemplate {
 
     const impl = Tag.impls[token.name]
     assert(impl, `tag ${token.name} not found`)
-    this.impl = create<ITagImplOptions, ITagImpl>(impl)
+
+    this.impl = Object.create(impl)
     this.impl.liquid = liquid
     if (this.impl.parse) {
       this.impl.parse(token, tokens)
@@ -30,11 +31,7 @@ export default class Tag extends Template<TagToken> implements ITemplate {
   async render (ctx: Context) {
     const hash = await Hash.create(this.token.args, ctx)
     const impl = this.impl
-    if (typeof impl.render !== 'function') {
-      return ''
-    }
-    const html = await impl.render(ctx, hash)
-    return stringify(html)
+    return isFunction(impl.render) ? stringify(await impl.render(ctx, hash)) : ''
   }
   static register (name: string, tag: ITagImplOptions) {
     Tag.impls[name] = tag
diff --git a/src/template/value.ts b/src/template/value.ts
index d4301a20b1..cfa064c9f8 100644
--- a/src/template/value.ts
+++ b/src/template/value.ts
@@ -4,8 +4,8 @@ import Context from '../context/context'
 
 export default class Value {
   private strictFilters: boolean
-  initial: string
-  filters: Array<Filter> = []
+  private initial: string
+  private filters: Array<Filter> = []
 
   /**
    * @param str value string, like: "i have a dream | truncate: 3
diff --git a/src/util/assert.ts b/src/util/assert.ts
index 243ac788f4..d469f045ea 100644
--- a/src/util/assert.ts
+++ b/src/util/assert.ts
@@ -1,6 +1,6 @@
 import { AssertionError } from './error'
 
-export default function (predicate: any, message?: string) {
+export default function<T> (predicate: T | null | undefined, message?: string) {
   if (!predicate) {
     message = message || `expect ${predicate} to be true`
     throw new AssertionError(message)
diff --git a/src/util/underscore.ts b/src/util/underscore.ts
index 7de9c1c63c..8612e459a5 100644
--- a/src/util/underscore.ts
+++ b/src/util/underscore.ts
@@ -36,10 +36,6 @@ export function toLiquid (value: any): any {
   return value
 }
 
-export function create<T1 extends object, T2 extends T1 = T1> (proto: T1): T2 {
-  return Object.create(proto)
-}
-
 export function isNil (value: any): boolean {
   return value === null || value === undefined
 }
diff --git a/test/unit/context/context.ts b/test/unit/context/context.ts
index af2a261b85..1f21773a8e 100644
--- a/test/unit/context/context.ts
+++ b/test/unit/context/context.ts
@@ -5,7 +5,7 @@ import { Scope } from '../../../src/context/scope'
 const expect = chai.expect
 
 describe('scope', function () {
-  let ctx: Context, scope: Scope
+  let ctx: any, scope: Scope
   beforeEach(function () {
     scope = {
       foo: 'zoo',
diff --git a/test/unit/template/value.ts b/test/unit/template/value.ts
index 381b291737..a5f824e0d6 100644
--- a/test/unit/template/value.ts
+++ b/test/unit/template/value.ts
@@ -14,70 +14,70 @@ describe('Value', function () {
 
   describe('#constructor()', function () {
     it('should parse "foo', function () {
-      const tpl = new Value('foo', false)
+      const tpl = new Value('foo', false) as any
       expect(tpl.initial).to.equal('foo')
       expect(tpl.filters).to.deep.equal([])
     })
 
     it('should parse "foo | add"', function () {
-      const tpl = new Value('foo | add', false)
+      const tpl = new Value('foo | add', false) as any
       expect(tpl.initial).to.equal('foo')
       expect(tpl.filters.length).to.equal(1)
       expect(tpl.filters[0].args).to.eql([])
     })
     it('should parse "foo,foo | add"', function () {
-      const tpl = new Value('foo,foo | add', false)
-      expect(tpl.initial).to.equal('foo')
+      const tpl = new Value('foo,foo | add', false) as any
+      expect(tpl.initial).to.equal('foo') as any
       expect(tpl.filters.length).to.equal(1)
       expect(tpl.filters[0].args).to.eql([])
     })
     it('should parse "foo | add: 3, false"', function () {
-      const tpl = new Value('foo | add: 3, "foo"', false)
+      const tpl = new Value('foo | add: 3, "foo"', false) as any
       expect(tpl.initial).to.equal('foo')
       expect(tpl.filters.length).to.equal(1)
       expect(tpl.filters[0].args).to.eql(['3', '"foo"'])
     })
     it('should parse "foo | add: "foo" bar, 3"', function () {
-      const tpl = new Value('foo | add: "foo" bar, 3', false)
+      const tpl = new Value('foo | add: "foo" bar, 3', false) as any
       expect(tpl.initial).to.equal('foo')
       expect(tpl.filters.length).to.equal(1)
       expect(tpl.filters[0].name).to.eql('add')
       expect(tpl.filters[0].args).to.eql(['"foo"', '3'])
     })
     it('should parse "foo | add: "|", 3', function () {
-      const tpl = new Value('foo | add: "|", 3', false)
+      const tpl = new Value('foo | add: "|", 3', false) as any
       expect(tpl.initial).to.equal('foo')
       expect(tpl.filters.length).to.equal(1)
       expect(tpl.filters[0].args).to.eql(['"|"', '3'])
     })
     it('should parse "foo | add: "|", 3', function () {
-      const tpl = new Value('foo | add: "|", 3', false)
+      const tpl = new Value('foo | add: "|", 3', false) as any
       expect(tpl.initial).to.equal('foo')
       expect(tpl.filters.length).to.equal(1)
       expect(tpl.filters[0].args).to.eql(['"|"', '3'])
     })
     it('should support arguments as named key/values', function () {
-      const f = new Value('o | foo: key1: "literal1", key2: value2', false)
+      const f = new Value('o | foo: key1: "literal1", key2: value2', false) as any
       expect(f.filters[0].name).to.equal('foo')
       expect(f.filters[0].args).to.eql([['key1', '"literal1"'], ['key2', 'value2']])
     })
     it('should support arguments as named key/values with inline literals', function () {
-      const f = new Value('o | foo: "test0", key1: "literal1", key2: value2', false)
+      const f = new Value('o | foo: "test0", key1: "literal1", key2: value2', false) as any
       expect(f.filters[0].name).to.equal('foo')
       expect(f.filters[0].args).to.deep.equal(['"test0"', ['key1', '"literal1"'], ['key2', 'value2']])
     })
     it('should support arguments as named key/values with inline values', function () {
-      const f = new Value('o | foo: test0, key1: "literal1", key2: value2', false)
+      const f = new Value('o | foo: test0, key1: "literal1", key2: value2', false) as any
       expect(f.filters[0].name).to.equal('foo')
       expect(f.filters[0].args).to.deep.equal(['test0', ['key1', '"literal1"'], ['key2', 'value2']])
     })
     it('should support argument values named same as keys', function () {
-      const f = new Value('o | foo: a: a', false)
+      const f = new Value('o | foo: a: a', false) as any
       expect(f.filters[0].name).to.equal('foo')
       expect(f.filters[0].args).to.deep.equal([['a', 'a']])
     })
     it('should support argument literals named same as keys', function () {
-      const f = new Value('o | foo: a: "a"', false)
+      const f = new Value('o | foo: a: "a"', false) as any
       expect(f.filters[0].name).to.equal('foo')
       expect(f.filters[0].args).to.deep.equal([['a', '"a"']])
     })