diff --git a/rollup.config.mjs b/rollup.config.mjs
index 328505fdc..ca7261f10 100644
--- a/rollup.config.mjs
+++ b/rollup.config.mjs
@@ -23,7 +23,8 @@ const tsconfig = (target) => ({
     compilerOptions: {
       target,
       module: 'ES2015',
-      rootDir: 'src'
+      rootDir: 'src',
+      downlevelIteration: true
     }
   }
 })
diff --git a/src/context/context.ts b/src/context/context.ts
index 083a17cfe..b8951056f 100644
--- a/src/context/context.ts
+++ b/src/context/context.ts
@@ -13,7 +13,7 @@ export class Context {
    * for tags like `{% capture %}` `{% assign %}` to operate
    */
   private scopes: Scope[] = [createScope()]
-  private registers = {}
+  private registers: Record<string, any> = {}
   /**
    * user passed in scope
    * `{% increment %}`, `{% decrement %}` changes this scope,
diff --git a/src/drop/drop.ts b/src/drop/drop.ts
index c62768dc2..f83f5576e 100644
--- a/src/drop/drop.ts
+++ b/src/drop/drop.ts
@@ -1,6 +1,7 @@
 import { Context } from '../context'
 
 export abstract class Drop {
+  [key: string]: any
   public liquidMethodMissing (key: string | number, context: Context): Promise<any> | any {
     return undefined
   }
diff --git a/src/filters/html.ts b/src/filters/html.ts
index 21cb8c4a9..807c42373 100644
--- a/src/filters/html.ts
+++ b/src/filters/html.ts
@@ -1,14 +1,14 @@
 import { FilterImpl } from '../template'
 import { stringify } from '../util/underscore'
 
-const escapeMap = {
+const escapeMap: Record<string, string> = {
   '&': '&amp;',
   '<': '&lt;',
   '>': '&gt;',
   '"': '&#34;',
   "'": '&#39;'
 }
-const unescapeMap = {
+const unescapeMap: Record<string, string> = {
   '&amp;': '&',
   '&lt;': '<',
   '&gt;': '>',
diff --git a/src/parser/tokenizer.ts b/src/parser/tokenizer.ts
index 0c2d86df7..be8ac136b 100644
--- a/src/parser/tokenizer.ts
+++ b/src/parser/tokenizer.ts
@@ -1,6 +1,6 @@
 import { FilteredValueToken, TagToken, HTMLToken, HashToken, QuotedToken, LiquidTagToken, OutputToken, ValueToken, Token, RangeToken, FilterToken, TopLevelToken, PropertyAccessToken, OperatorToken, LiteralToken, IdentifierToken, NumberToken } from '../tokens'
 import { OperatorHandler } from '../render/operator'
-import { TrieNode, LiteralValue, Trie, createTrie, ellipsis, literalValues, TokenizationError, TYPES, QUOTE, BLANK, NUMBER, SIGN, isWord, isString } from '../util'
+import { LiteralValue, Trie, createTrie, ellipsis, literalValues, TokenizationError, TYPES, QUOTE, BLANK, NUMBER, SIGN, isWord, isString } from '../util'
 import { Operators, Expression } from '../render'
 import { NormalizedFullOptions, defaultOptions } from '../liquid-options'
 import { FilterArg } from './filter-arg'
@@ -51,11 +51,11 @@ export class Tokenizer {
     return new OperatorToken(this.input, this.p, (this.p = end), this.file)
   }
   matchTrie<T> (trie: Trie<T>) {
-    let node: TrieNode<T> = trie
+    let node: Trie<T> = trie
     let i = this.p
-    let info
-    while (node[this.input[i]] && i < this.N) {
-      node = node[this.input[i++]]
+    let info: Trie<T> | undefined
+    while ((node as Trie<T>)[this.input[i]] && i < this.N) {
+      node = (node as Trie<T>)[this.input[i++]] as Trie<T>
       if (node['end']) info = node
     }
     if (!info) return -1
diff --git a/src/render/string.ts b/src/render/string.ts
index c1e8f1a3e..91b726367 100644
--- a/src/render/string.ts
+++ b/src/render/string.ts
@@ -1,6 +1,6 @@
 const rHex = /[\da-fA-F]/
 const rOct = /[0-7]/
-const escapeChar = {
+const escapeChar: Record<string, string> = {
   b: '\b',
   f: '\f',
   n: '\n',
diff --git a/src/tags/for.ts b/src/tags/for.ts
index fec0b0603..198750116 100644
--- a/src/tags/for.ts
+++ b/src/tags/for.ts
@@ -52,7 +52,7 @@ export default class extends Tag {
 
     const continueKey = 'continue-' + this.variable + '-' + this.collection.getText()
     ctx.push(createScope({ continue: ctx.getRegister(continueKey, {}) }))
-    const hash = yield this.hash.render(ctx)
+    const hash = (yield this.hash.render(ctx)) as Record<string, any>
     ctx.pop()
 
     const modifiers = this.liquid.options.orderedFilterParameters
diff --git a/src/tags/include.ts b/src/tags/include.ts
index 0db1ee749..a00dda4e2 100644
--- a/src/tags/include.ts
+++ b/src/tags/include.ts
@@ -3,16 +3,18 @@ import { BlockMode, createScope, Scope } from '../context'
 import { Parser } from '../parser'
 import { Argument, Arguments, PartialScope } from '../template'
 import { isString, isValueToken } from '../util'
-import { parseFilePath, renderFilePath } from './render'
+import { parseFilePath, renderFilePath, ParsedFileName } from './render'
 
 export default class extends Tag {
+  private file: ParsedFileName
+  private currentFile?: string
   private withVar?: ValueToken
   private hash: Hash
   constructor (token: TagToken, remainTokens: TopLevelToken[], liquid: Liquid, parser: Parser) {
     super(token, remainTokens, liquid)
     const { tokenizer } = token
-    this['file'] = parseFilePath(tokenizer, this.liquid, parser)
-    this['currentFile'] = token.file
+    this.file = parseFilePath(tokenizer, this.liquid, parser)
+    this.currentFile = token.file
 
     const begin = tokenizer.p
     const withStr = tokenizer.readIdentifier()
@@ -28,7 +30,7 @@ export default class extends Tag {
   * render (ctx: Context, emitter: Emitter): Generator<unknown, void, unknown> {
     const { liquid, hash, withVar } = this
     const { renderer } = liquid
-    const filepath = (yield renderFilePath(this['file'], ctx, liquid)) as string
+    const filepath = (yield renderFilePath(this.file, ctx, liquid)) as string
     assert(filepath, () => `illegal file path "${filepath}"`)
 
     const saved = ctx.saveRegister('blocks', 'blockMode')
@@ -36,7 +38,7 @@ export default class extends Tag {
     ctx.setRegister('blockMode', BlockMode.OUTPUT)
     const scope = createScope((yield hash.render(ctx)) as Scope)
     if (withVar) scope[filepath] = yield evalToken(withVar, ctx)
-    const templates = (yield liquid._parsePartialFile(filepath, ctx.sync, this['currentFile'])) as Template[]
+    const templates = (yield liquid._parsePartialFile(filepath, ctx.sync, this.currentFile)) as Template[]
     ctx.push(ctx.opts.jekyllInclude ? createScope({ include: scope }) : scope)
     yield renderer.renderTemplates(templates, ctx, emitter)
     ctx.pop()
@@ -44,14 +46,14 @@ export default class extends Tag {
   }
 
   public * children (partials: boolean, sync: boolean): Generator<unknown, Template[]> {
-    if (partials && isString(this['file'])) {
-      return (yield this.liquid._parsePartialFile(this['file'], sync, this['currentFile'])) as Template[]
+    if (partials && isString(this.file)) {
+      return (yield this.liquid._parsePartialFile(this.file, sync, this.currentFile)) as Template[]
     }
     return []
   }
 
   public partialScope (): PartialScope | undefined {
-    if (isString(this['file'])) {
+    if (isString(this.file)) {
       let names: Array<string | [string, Argument]>
 
       if (this.liquid.options.jekyllInclude) {
@@ -59,19 +61,19 @@ export default class extends Tag {
       } else {
         names = Object.keys(this.hash.hash)
         if (this.withVar) {
-          names.push([this['file'], this.withVar])
+          names.push([this.file, this.withVar])
         }
       }
 
-      return { name: this['file'], isolated: false, scope: names }
+      return { name: this.file, isolated: false, scope: names }
     }
   }
 
   public * arguments (): Arguments {
     yield * Object.values(this.hash.hash).filter(isValueToken)
 
-    if (isValueToken(this['file'])) {
-      yield this['file']
+    if (isValueToken(this.file)) {
+      yield this.file
     }
 
     if (isValueToken(this.withVar)) {
diff --git a/src/tags/layout.ts b/src/tags/layout.ts
index ab2b3b539..156ab0ee4 100644
--- a/src/tags/layout.ts
+++ b/src/tags/layout.ts
@@ -10,10 +10,11 @@ export default class extends Tag {
   args: Hash
   templates: Template[]
   file?: ParsedFileName
+  private currentFile?: string
   constructor (token: TagToken, remainTokens: TopLevelToken[], liquid: Liquid, parser: Parser) {
     super(token, remainTokens, liquid)
     this.file = parseFilePath(this.tokenizer, this.liquid, parser)
-    this['currentFile'] = token.file
+    this.currentFile = token.file
     this.args = new Hash(this.tokenizer, liquid.options.keyValueSeparator)
     this.templates = parser.parseTokens(remainTokens)
   }
@@ -27,7 +28,7 @@ export default class extends Tag {
     }
     const filepath = (yield renderFilePath(this.file, ctx, liquid)) as string
     assert(filepath, () => `illegal file path "${filepath}"`)
-    const templates = (yield liquid._parseLayoutFile(filepath, ctx.sync, this['currentFile'])) as Template[]
+    const templates = (yield liquid._parseLayoutFile(filepath, ctx.sync, this.currentFile)) as Template[]
 
     // render remaining contents and store rendered results
     ctx.setRegister('blockMode', BlockMode.STORE)
@@ -48,7 +49,7 @@ export default class extends Tag {
     const templates = this.templates.slice()
 
     if (partials && isString(this.file)) {
-      templates.push(...(yield this.liquid._parsePartialFile(this.file, true, this['currentFile'])) as Template[])
+      templates.push(...(yield this.liquid._parsePartialFile(this.file, true, this.currentFile)) as Template[])
     }
 
     return templates
diff --git a/src/tags/render.ts b/src/tags/render.ts
index 123e73a93..bf86a28cb 100644
--- a/src/tags/render.ts
+++ b/src/tags/render.ts
@@ -1,16 +1,20 @@
 import { __assign } from 'tslib'
 import { ForloopDrop } from '../drop'
 import { isString, isValueToken, toEnumerable } from '../util'
-import { TopLevelToken, assert, Liquid, Token, Template, evalQuotedToken, TypeGuards, Tokenizer, evalToken, Hash, Emitter, TagToken, Context, Tag } from '..'
+import { TopLevelToken, assert, Liquid, Token, ValueToken, Template, evalQuotedToken, TypeGuards, Tokenizer, evalToken, Hash, Emitter, TagToken, Context, Tag } from '..'
 import { Parser } from '../parser'
 import { Argument, Arguments, PartialScope } from '../template'
 
 export type ParsedFileName = Template[] | Token | string | undefined
 
+type RenderBinding = { value: ValueToken; alias?: string }
+
 export default class extends Tag {
   private file: ParsedFileName
   private currentFile?: string
   private hash: Hash
+  private with?: RenderBinding
+  private forBinding?: RenderBinding
   constructor (token: TagToken, remainTokens: TopLevelToken[], liquid: Liquid, parser: Parser) {
     super(token, remainTokens, liquid)
     const tokenizer = this.tokenizer
@@ -33,7 +37,9 @@ export default class extends Tag {
             if (asStr.content === 'as') alias = tokenizer.readIdentifier()
             else tokenizer.p = beforeAs
 
-            this[keyword.content] = { value, alias: alias && alias.content }
+            const binding: RenderBinding = { value, alias: alias && alias.content }
+            if (keyword.content === 'with') this.with = binding
+            else this.forBinding = binding
             tokenizer.skipBlank()
             if (tokenizer.peek() === ',') tokenizer.advance()
             continue // matched!
@@ -50,46 +56,46 @@ export default class extends Tag {
   }
   * render (ctx: Context, emitter: Emitter): Generator<unknown, void, unknown> {
     const { liquid, hash } = this
-    const filepath = (yield renderFilePath(this['file'], ctx, liquid)) as string
+    const filepath = (yield renderFilePath(this.file, ctx, liquid)) as string
     assert(filepath, () => `illegal file path "${filepath}"`)
 
     const childCtx = ctx.spawn()
     const scope = childCtx.bottom()
     __assign(scope, yield hash.render(ctx))
-    if (this['with']) {
-      const { value, alias } = this['with']
+    if (this.with) {
+      const { value, alias } = this.with
       scope[alias || filepath] = yield evalToken(value, ctx)
     }
 
-    if (this['for']) {
-      const { value, alias } = this['for']
+    if (this.forBinding) {
+      const { value, alias } = this.forBinding
       const collection = toEnumerable(yield evalToken(value, ctx))
-      scope['forloop'] = new ForloopDrop(collection.length, value.getText(), alias)
+      scope['forloop'] = new ForloopDrop(collection.length, value.getText(), alias as string)
       for (const item of collection) {
-        scope[alias] = item
-        const templates = (yield liquid._parsePartialFile(filepath, childCtx.sync, this['currentFile'])) as Template[]
+        scope[alias as string] = item
+        const templates = (yield liquid._parsePartialFile(filepath, childCtx.sync, this.currentFile)) as Template[]
         yield liquid.renderer.renderTemplates(templates, childCtx, emitter)
         scope['forloop'].next()
       }
     } else {
-      const templates = (yield liquid._parsePartialFile(filepath, childCtx.sync, this['currentFile'])) as Template[]
+      const templates = (yield liquid._parsePartialFile(filepath, childCtx.sync, this.currentFile)) as Template[]
       yield liquid.renderer.renderTemplates(templates, childCtx, emitter)
     }
   }
 
   public * children (partials: boolean, sync: boolean): Generator<unknown, Template[]> {
-    if (partials && isString(this['file'])) {
-      return (yield this.liquid._parsePartialFile(this['file'], sync, this['currentFile'])) as Template[]
+    if (partials && isString(this.file)) {
+      return (yield this.liquid._parsePartialFile(this.file, sync, this.currentFile)) as Template[]
     }
     return []
   }
 
   public partialScope (): PartialScope | undefined {
-    if (isString(this['file'])) {
+    if (isString(this.file)) {
       const names: Array<string | [string, Argument]> = Object.keys(this.hash.hash)
 
-      if (this['with']) {
-        const { value, alias } = this['with']
+      if (this.with) {
+        const { value, alias } = this.with
         if (isString(alias)) {
           names.push([alias, value])
         } else if (isString(this.file)) {
@@ -97,8 +103,8 @@ export default class extends Tag {
         }
       }
 
-      if (this['for']) {
-        const { value, alias } = this['for']
+      if (this.forBinding) {
+        const { value, alias } = this.forBinding
         if (isString(alias)) {
           names.push([alias, value])
         } else if (isString(this.file)) {
@@ -106,7 +112,7 @@ export default class extends Tag {
         }
       }
 
-      return { name: this['file'], isolated: true, scope: names }
+      return { name: this.file, isolated: true, scope: names }
     }
   }
 
@@ -117,15 +123,15 @@ export default class extends Tag {
       }
     }
 
-    if (this['with']) {
-      const { value } = this['with']
+    if (this.with) {
+      const { value } = this.with
       if (isValueToken(value)) {
         yield value
       }
     }
 
-    if (this['for']) {
-      const { value } = this['for']
+    if (this.forBinding) {
+      const { value } = this.forBinding
       if (isValueToken(value)) {
         yield value
       }
diff --git a/src/template/hash.ts b/src/template/hash.ts
index 4899a8045..4ef67c1a2 100644
--- a/src/template/hash.ts
+++ b/src/template/hash.ts
@@ -24,7 +24,7 @@ export class Hash {
   }
 
   * render (ctx: Context): Generator<unknown, Record<string, any>, unknown> {
-    const hash = {}
+    const hash: Record<string, any> = {}
     for (const key of Object.keys(this.hash)) {
       hash[key] = this.hash[key] === undefined ? true : yield evalToken(this.hash[key], ctx)
     }
diff --git a/src/tokens/literal-token.ts b/src/tokens/literal-token.ts
index 2852e2e02..ce60fdfc5 100644
--- a/src/tokens/literal-token.ts
+++ b/src/tokens/literal-token.ts
@@ -1,10 +1,10 @@
 import { Token } from './token'
 import { TokenKind } from '../parser'
-import { literalValues, LiteralValue } from '../util'
+import { literalValues, LiteralValue, LiteralKey } from '../util'
 
 export class LiteralToken extends Token {
   public content: LiteralValue
-  public literal: string
+  public literal: LiteralKey
   public constructor (
     public input: string,
     public begin: number,
@@ -12,7 +12,7 @@ export class LiteralToken extends Token {
     public file?: string
   ) {
     super(TokenKind.Literal, input, begin, end, file)
-    this.literal = this.getText()
+    this.literal = this.getText() as LiteralKey
     this.content = literalValues[this.literal]
   }
 }
diff --git a/src/tokens/operator-token.ts b/src/tokens/operator-token.ts
index ae6724e22..358878278 100644
--- a/src/tokens/operator-token.ts
+++ b/src/tokens/operator-token.ts
@@ -32,8 +32,10 @@ export const operatorTypes = {
   'or': OperatorType.Binary
 }
 
+export type OperatorKey = keyof typeof operatorPrecedences
+
 export class OperatorToken extends Token {
-  public operator: string
+  public operator: OperatorKey
   public constructor (
     public input: string,
     public begin: number,
@@ -41,10 +43,9 @@ export class OperatorToken extends Token {
     public file?: string
   ) {
     super(TokenKind.Operator, input, begin, end, file)
-    this.operator = this.getText()
+    this.operator = this.getText() as OperatorKey
   }
   getPrecedence () {
-    const key = this.getText()
-    return key in operatorPrecedences ? operatorPrecedences[key] : 1
+    return this.operator in operatorPrecedences ? operatorPrecedences[this.operator] : 1
   }
 }
diff --git a/src/util/async.ts b/src/util/async.ts
index c190cd860..137753ded 100644
--- a/src/util/async.ts
+++ b/src/util/async.ts
@@ -18,10 +18,10 @@ export async function toPromise<T> (val: Generator<unknown, T, unknown> | Promis
   if (!isIterator(val)) return val
   let value: unknown
   let done = false
-  let next = 'next'
+  let next: 'next' | 'throw' = 'next'
   do {
     const state = val[next](value)
-    done = state.done
+    done = !!state.done
     value = state.value
     next = 'next'
     try {
@@ -40,10 +40,10 @@ export function toValueSync<T> (val: Generator<unknown, T, unknown> | T): T {
   if (!isIterator(val)) return val
   let value: any
   let done = false
-  let next = 'next'
+  let next: 'next' | 'throw' = 'next'
   do {
     const state = val[next](value)
-    done = state.done
+    done = !!state.done
     value = state.value
     next = 'next'
     if (isIterator(value)) {
diff --git a/src/util/error.ts b/src/util/error.ts
index 8fe76061d..3b5534bab 100644
--- a/src/util/error.ts
+++ b/src/util/error.ts
@@ -29,7 +29,7 @@ export abstract class LiquidError extends Error {
     if (this.originalError) this.stack += '\nFrom ' + this.originalError.stack
   }
   static is (obj: unknown): obj is LiquidError {
-    return obj?.[TRAIT] === 'LiquidError'
+    return (obj as Record<string, unknown> | null | undefined)?.[TRAIT] === 'LiquidError'
   }
 }
 
diff --git a/src/util/operator-trie.ts b/src/util/operator-trie.ts
index e09c90ef0..f94d7138a 100644
--- a/src/util/operator-trie.ts
+++ b/src/util/operator-trie.ts
@@ -4,22 +4,16 @@ interface TrieInput<T> {
   [key: string]: T
 }
 
-interface TrieLeafNode<T> {
-  data: T;
-  end: true;
-  needBoundary?: true;
-}
-
-export interface Trie<T> {
-  [key: string]: Trie<T> | TrieLeafNode<T>;
-}
-
-export type TrieNode<T> = Trie<T> | TrieLeafNode<T>
+export type Trie<T> = {
+  data?: T
+  end?: true
+  needBoundary?: true
+} & Record<string, any>
 
 export function createTrie<T = any> (input: TrieInput<T>): Trie<T> {
   const trie: Trie<T> = {}
   for (const [name, data] of Object.entries(input)) {
-    let node: Trie<T> | TrieLeafNode<T> = trie
+    let node = trie
 
     for (let i = 0; i < name.length; i++) {
       const c = name[i]
diff --git a/src/util/strftime.ts b/src/util/strftime.ts
index e6ac04ebf..8bf8b09d1 100644
--- a/src/util/strftime.ts
+++ b/src/util/strftime.ts
@@ -4,7 +4,7 @@ import type { Limiter } from './limiter'
 
 const rFormat = /%([-_0^#:]+)?(\d+)?([EO])?(.)/
 interface FormatOptions {
-  flags: object;
+  flags: Record<string, boolean>;
   width?: string;
   modifier?: string;
   memoryLimit?: Pick<Limiter, 'use'>;
@@ -50,7 +50,7 @@ function century (d: LiquidDate) {
 }
 
 // default to 0
-const padWidths = {
+const padWidths: Record<string, number> = {
   d: 2,
   e: 2,
   H: 2,
@@ -77,7 +77,9 @@ function getTimezoneOffset (d: LiquidDate, opts: FormatOptions) {
     (opts.flags[':'] ? ':' : '') +
     padStart(m, 2, '0')
 }
-const formatCodes = {
+type FormatCodeHandler = (d: LiquidDate, opts: FormatOptions) => unknown
+
+const formatCodes: Record<string, FormatCodeHandler> = {
   a: (d: LiquidDate) => d.getShortWeekdayName(),
   A: (d: LiquidDate) => d.getLongWeekdayName(),
   b: (d: LiquidDate) => d.getShortMonthName(),
@@ -118,8 +120,8 @@ const formatCodes = {
   't': () => '\t',
   'n': () => '\n',
   '%': () => '%'
-};
-(formatCodes as any).h = formatCodes.b
+}
+formatCodes.h = formatCodes.b
 
 export function strftime (d: LiquidDate, formatStr: string, memoryLimit?: Pick<Limiter, 'use'>) {
   let output = ''
@@ -137,11 +139,11 @@ function format (d: LiquidDate, match: RegExpExecArray, memoryLimit?: Pick<Limit
   const [input, flagStr = '', width, modifier, conversion] = match
   const convert = formatCodes[conversion]
   if (!convert) return input
-  const flags = {}
+  const flags: Record<string, boolean> = {}
   for (const flag of flagStr) flags[flag] = true
   let ret = String(convert(d, { flags, width, modifier, memoryLimit }))
   let padChar = padSpaceChars.has(conversion) ? ' ' : '0'
-  let padWidth = width || padWidths[conversion] || 0
+  let padWidth = Number(width) || padWidths[conversion] || 0
   if (flags['^']) ret = ret.toUpperCase()
   else if (flags['#']) ret = changeCase(ret)
   if (flags['_']) padChar = ' '
diff --git a/test/integration/liquid/liquid.spec.ts b/test/integration/liquid/liquid.spec.ts
index 918b1aabe..e229940a2 100644
--- a/test/integration/liquid/liquid.spec.ts
+++ b/test/integration/liquid/liquid.spec.ts
@@ -1,6 +1,7 @@
 import { Liquid, Context, isFalsy } from '../../../src'
 import { mock, restore } from '../../stub/mockfs'
 import { drainStream } from '../../stub/stream'
+import { resolve } from 'path'
 
 describe('Liquid', function () {
   describe('#plugin()', function () {
@@ -144,7 +145,7 @@ describe('Liquid', function () {
     })
     it('should fallback to require.resolve in Node.js', async function () {
       const engine = new Liquid({
-        root: [process.cwd()],
+        root: [resolve(__dirname, '../../..')],
         extname: '.html'
       })
       const tpls = await engine.parseFileSync('jest')
diff --git a/tsconfig.json b/tsconfig.json
index 258f536b4..0646fbcfe 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -9,9 +9,7 @@
     "skipLibCheck": true,
     "allowSyntheticDefaultImports": true,
     "resolveJsonModule": true,
-    "downlevelIteration": true,
-    "strict": true,
-    "suppressImplicitAnyIndexErrors": true
+    "strict": true
   },
   "all": true,
   "exclude": [ "node_modules", "dist", "demo", "test" ]