diff --git a/src/driver/connect.ts b/src/driver/connect.ts
index abafee3..89ccde3 100644
--- a/src/driver/connect.ts
+++ b/src/driver/connect.ts
@@ -1,16 +1,9 @@
 import * as React from 'react'
 
-export type ParametersOfReturnedFunction<Func> = Func extends (<Args extends []>(
-  ...args1: any[] // it's ok
-) => (...args2: Args) => any) // it's ok
-  ? Args
-  : never
-
-export type Method = (...args: Args) => void | Promise<void>
-type Args = any[] // it's ok
+export type Method<Args = any[]> = (...args: Args extends any[] ? Args : []) => void | Promise<void>
 export type Middleware = <M extends Method, MM extends Method>(
   method: M,
-  args: Parameters<M>
+  args: Parameters<M>,
 ) => [MM | M, Parameters<MM | M>]
 
 const middlewares: Middleware[] = []
@@ -40,11 +33,11 @@ function run<M extends Method>([method, args]: [M, Parameters<M>]) {
 export type DispatchState<Props, State> = React.Component<Props, State>['setState']
 export type PreDispatch<Props, State> = (
   dispatchCallback: (state: State, props: Props) => Props | Promise<void> | void,
-  callback?: () => void
+  callback?: () => void,
 ) => void
-export type TriggerOtherMethod = <MC extends MethodCreator<any, any>>(
+export type TriggerOtherMethod = <MC extends MethodCreator<any, any, any[]>>(
   methodCreator: MC,
-  ...args: ParametersOfReturnedFunction<MC>
+  ...args: Parameters<ReturnType<MC>>
 ) => void
 
 export type Dispatch<Props, State> = {
@@ -53,20 +46,25 @@ export type Dispatch<Props, State> = {
   call: TriggerOtherMethod
 }
 
-export type MethodCreator<Props, State> = (dispatch: Dispatch<Props, State>) => Method
+export type MethodCreator<Props, State, Args = []> = (
+  dispatch: Dispatch<Props, State>,
+) => Method<Args>
 
-type Sources = {
-  [key: string]: MethodCreator<any, any>
+type Sources<P, S> = {
+  [key: string]: MethodCreator<P, S, any[]>
 }
 type WrappedMethods = {
   [key: string]: Method
 }
 
-function link<P, S>(instance: React.Component<P, S>, sources: Sources): WrappedMethods {
+function link<P, S>(instance: React.Component<P, S>, sources: Sources<P, S>): WrappedMethods {
   const wrappedMethods: WrappedMethods = {
     /* [keyof sources] -> wrappedMethods.method */
   }
-  const map = new Map<MethodCreator<P, S>, Method>(/* sources.creator -> wrappedMethods.method */)
+  const map = new Map<
+    MethodCreator<P, S, any[]>,
+    Method
+  >(/* sources.creator -> wrappedMethods.method */)
 
   const dispatchCall: TriggerOtherMethod = (createMethod, ...otherArgs) => {
     const isFromSource = sourcesValues.includes(createMethod)
@@ -99,9 +97,9 @@ function link<P, S>(instance: React.Component<P, S>, sources: Sources): WrappedM
   return wrappedMethods
 }
 
-export default function connect<BaseP, ExtraP>(mapping: Sources) {
+export default function connect<BaseP, ExtraP>(mapping: Sources<BaseP, ExtraP>) {
   return function linkComponent<S>(
-    ComponentClass: React.ComponentClass<BaseP & ExtraP, S>
+    ComponentClass: React.ComponentClass<BaseP & ExtraP, S>,
   ): React.ComponentClass<BaseP, ExtraP> {
     return class AwesomeApp extends React.PureComponent<BaseP, ExtraP> {
       static displayName = `Connected(${ComponentClass.displayName || ComponentClass.name})`
diff --git a/src/driver/core/FileExplorer.ts b/src/driver/core/FileExplorer.ts
index 461ae93..06a5adf 100644
--- a/src/driver/core/FileExplorer.ts
+++ b/src/driver/core/FileExplorer.ts
@@ -39,7 +39,8 @@ type Task = () => void
 const tasksAfterRender: (Task)[] = []
 const visibleNodesGenerator = new VisibleNodesGenerator()
 
-const init: MethodCreator<Props, ConnectorState> = dispatch => () => dispatch.call(setStateText, 'Fetching File List...')
+const init: MethodCreator<Props, ConnectorState> = dispatch => () =>
+  dispatch.call(setStateText, 'Fetching File List...')
 
 function resolveGitModules(root: TreeNode, blobData: BlobData) {
   if (blobData) {
@@ -79,7 +80,7 @@ const setUpTree: MethodCreator<Props, ConnectorState> = dispatch => () =>
     await visibleNodesGenerator.plantTree(root as TreeNode)
 
     tasksAfterRender.push(DOMHelper.focusSearchInput)
-    dispatch.call(setStateText, null)
+    dispatch.call(setStateText, '')
     const currentPath = URLHelper.getCurrentPath(metaData.branchName)
     if (currentPath.length) {
       const nodeExpandedTo = visibleNodesGenerator.expandTo(currentPath.join('/'))
@@ -99,12 +100,20 @@ const execAfterRender: MethodCreator<Props, ConnectorState> = dispatch => () =>
   tasksAfterRender.length = 0
 }
 
-const setStateText: MethodCreator<Props, ConnectorState> = dispatch => (text: string) =>
+const setStateText: MethodCreator<
+  Props,
+  ConnectorState,
+  [ConnectorState['stateText']]
+> = dispatch => (text: string) =>
   dispatch.set({
     stateText: text,
   })
 
-const handleKeyDown: MethodCreator<Props, ConnectorState> = dispatch => event =>
+const handleKeyDown: MethodCreator<
+  Props,
+  ConnectorState,
+  [React.KeyboardEvent]
+> = dispatch => event =>
   dispatch.get(({ visibleNodes: { nodes, focusedNode, expandedNodes, depths } }) => {
     function handleVerticalMove(index: number) {
       if (0 <= index && index < nodes.length) {
@@ -201,12 +210,17 @@ const handleKeyDown: MethodCreator<Props, ConnectorState> = dispatch => event =>
     }
   })
 
-const onFocusSearchBar: MethodCreator<Props, ConnectorState> = dispatch => () => dispatch.call(focusNode, null)
+const onFocusSearchBar: MethodCreator<Props, ConnectorState> = dispatch => () =>
+  dispatch.call(focusNode, null)
 
-const handleSearchKeyChange: MethodCreator<Props, ConnectorState> = dispatch => {
+const handleSearchKeyChange: MethodCreator<
+  Props,
+  ConnectorState,
+  [React.FormEvent<HTMLInputElement>]
+> = dispatch => {
   let i = 0
   return async event => {
-    const searchKey = event.target.value
+    const searchKey = event.currentTarget.value
     const j = (i += 1)
     await visibleNodesGenerator.search(searchKey)
     if (i === j) dispatch.call(updateVisibleNodes)
@@ -221,7 +235,10 @@ function shouldDelayExpand(node: TreeNode) {
   )
 }
 
-const setExpand: MethodCreator<Props, ConnectorState> = dispatch => (node, expand) => {
+const setExpand: MethodCreator<Props, ConnectorState, [TreeNode, boolean]> = dispatch => (
+  node,
+  expand = false
+) => {
   visibleNodesGenerator.setExpand(node, expand)
   const applyChanges = () => dispatch.call(focusNode, node)
   if (shouldDelayExpand(node)) {
@@ -232,7 +249,10 @@ const setExpand: MethodCreator<Props, ConnectorState> = dispatch => (node, expan
   }
 }
 
-const toggleNodeExpansion: MethodCreator<Props, ConnectorState> = dispatch => (node, skipScrollToNode) => {
+const toggleNodeExpansion: MethodCreator<Props, ConnectorState, [TreeNode, boolean]> = dispatch => (
+  node,
+  skipScrollToNode
+) => {
   visibleNodesGenerator.toggleExpand(node)
   const applyChanges = () => {
     dispatch.call(focusNode, node, skipScrollToNode)
@@ -246,7 +266,11 @@ const toggleNodeExpansion: MethodCreator<Props, ConnectorState> = dispatch => (n
   }
 }
 
-const focusNode: MethodCreator<Props, ConnectorState> = dispatch => (node, skipScroll) =>
+const focusNode: MethodCreator<
+  Props,
+  ConnectorState,
+  [TreeNode] | [TreeNode, boolean]
+> = dispatch => (node: TreeNode, skipScroll = false) =>
   dispatch.get(({ visibleNodes: { nodes } }) => {
     visibleNodesGenerator.focusNode(node)
     if (node && !skipScroll) {
@@ -257,7 +281,7 @@ const focusNode: MethodCreator<Props, ConnectorState> = dispatch => (node, skipS
     dispatch.call(updateVisibleNodes)
   })
 
-const onNodeClick: MethodCreator<Props, ConnectorState> = dispatch => node => {
+const onNodeClick: MethodCreator<Props, ConnectorState, [TreeNode]> = dispatch => node => {
   if (node.type === 'tree') {
     dispatch.call(toggleNodeExpansion, node, true)
   } else if (node.type === 'blob') {
@@ -268,7 +292,11 @@ const onNodeClick: MethodCreator<Props, ConnectorState> = dispatch => node => {
   }
 }
 
-const mountExpandingIndicator: MethodCreator<Props, ConnectorState> = dispatch => node =>
+const mountExpandingIndicator: MethodCreator<
+  Props,
+  ConnectorState,
+  [TreeNode]
+> = dispatch => node =>
   dispatch.get(({ visibleNodes }) => {
     const dummyVisibleNodes = {
       ...visibleNodes,
diff --git a/src/driver/core/SideBar.ts b/src/driver/core/SideBar.ts
index b9a06ea..02a601a 100644
--- a/src/driver/core/SideBar.ts
+++ b/src/driver/core/SideBar.ts
@@ -44,7 +44,7 @@ export type ConnectorState = {
   toggleShowSideBar: () => void
   toggleShowSettings: () => void
   onAccessTokenChange: SettingsBar['props']['onAccessTokenChange']
-  onKeyDown: EventListener
+  onKeyDown: (e: KeyboardEvent) => string
   onShortcutChange: SettingsBar['props']['onShortcutChange']
   setCopyFile: SettingsBar['props']['setCopyFile']
   setCopySnippet: SettingsBar['props']['setCopySnippet']
@@ -134,7 +134,7 @@ const init: MethodCreator<Props, ConnectorState> = dispatch => async () => {
   }
 }
 
-const handleError: MethodCreator<Props, ConnectorState> = dispatch => async err => {
+const handleError: MethodCreator<Props, ConnectorState, [Error]> = dispatch => async err => {
   if (err.message === EMPTY_PROJECT) {
     dispatch.call(setError, 'This project seems to be empty.')
   } else if (
@@ -160,7 +160,7 @@ const onPJAXEnd: MethodCreator<Props, ConnectorState> = dispatch => () => {
   })
 }
 
-const onKeyDown: MethodCreator<Props, ConnectorState> = dispatch => e => {
+const onKeyDown: MethodCreator<Props, ConnectorState, [KeyboardEvent]> = dispatch => e => {
   dispatch.get(({ toggleShowSideBarShortcut }) => {
     if (toggleShowSideBarShortcut) {
       const keys = keyHelper.parseEvent(e)
@@ -172,16 +172,22 @@ const onKeyDown: MethodCreator<Props, ConnectorState> = dispatch => e => {
 }
 
 const toggleShowSideBar: MethodCreator<Props, ConnectorState> = dispatch => () =>
-  dispatch.get(({ shouldShow }) =>
-    dispatch.call(setShouldShow, !shouldShow)
-  )
+  dispatch.get(({ shouldShow }) => dispatch.call(setShouldShow, !shouldShow))
 
-const setShouldShow: MethodCreator<Props, ConnectorState> = dispatch => shouldShow => {
+const setShouldShow: MethodCreator<
+  Props,
+  ConnectorState,
+  [ConnectorState['shouldShow']]
+> = dispatch => shouldShow => {
   dispatch.set({ shouldShow }, shouldShow ? DOMHelper.focusFileExplorer : null)
   DOMHelper.setBodyIndent(shouldShow)
 }
 
-const setError: MethodCreator<Props, ConnectorState> = dispatch => error => {
+const setError: MethodCreator<
+  Props,
+  ConnectorState,
+  [ConnectorState['error']]
+> = dispatch => error => {
   dispatch.set({ error })
   dispatch.call(setShouldShow, false)
 }
@@ -191,22 +197,47 @@ const toggleShowSettings: MethodCreator<Props, ConnectorState> = dispatch => ()
     showSettings: !showSettings,
   }))
 
-const setShowSettings: MethodCreator<Props, ConnectorState> = dispatch => showSettings => dispatch.set({ showSettings })
+const setShowSettings: MethodCreator<
+  Props,
+  ConnectorState,
+  [ConnectorState['showSettings']]
+> = dispatch => showSettings => dispatch.set({ showSettings })
 
-const onAccessTokenChange: MethodCreator<Props, ConnectorState> = dispatch => accessToken => dispatch.set({ accessToken })
+const onAccessTokenChange: MethodCreator<
+  Props,
+  ConnectorState,
+  [ConnectorState['accessToken']]
+> = dispatch => accessToken => dispatch.set({ accessToken })
 
-const onShortcutChange: MethodCreator<Props, ConnectorState> = dispatch => shortcut =>
-  dispatch.set({ toggleShowSideBarShortcut: shortcut })
+const onShortcutChange: MethodCreator<
+  Props,
+  ConnectorState,
+  [ConnectorState['toggleShowSideBarShortcut']]
+> = dispatch => shortcut => dispatch.set({ toggleShowSideBarShortcut: shortcut })
 
-const setMetaData: MethodCreator<Props, ConnectorState> = dispatch => metaData => dispatch.set({ metaData })
+const setMetaData: MethodCreator<
+  Props,
+  ConnectorState,
+  [ConnectorState['metaData']]
+> = dispatch => metaData => dispatch.set({ metaData })
 
-const setCompressSingleton: MethodCreator<Props, ConnectorState> = dispatch => compressSingletonFolder =>
-  dispatch.set({ compressSingletonFolder })
+const setCompressSingleton: MethodCreator<
+  Props,
+  ConnectorState,
+  [ConnectorState['compressSingletonFolder']]
+> = dispatch => compressSingletonFolder => dispatch.set({ compressSingletonFolder })
 
-const setCopyFile: MethodCreator<Props, ConnectorState> = dispatch => copyFileButton => dispatch.set({ copyFileButton })
+const setCopyFile: MethodCreator<
+  Props,
+  ConnectorState,
+  [ConnectorState['copyFileButton']]
+> = dispatch => copyFileButton => dispatch.set({ copyFileButton })
 
-const setCopySnippet: MethodCreator<Props, ConnectorState> = dispatch => copySnippetButton =>
-  dispatch.set({ copySnippetButton })
+const setCopySnippet: MethodCreator<
+  Props,
+  ConnectorState,
+  [ConnectorState['copySnippetButton']]
+> = dispatch => copySnippetButton => dispatch.set({ copySnippetButton })
 
 export default {
   init,
diff --git a/src/utils/DOMHelper.ts b/src/utils/DOMHelper.ts
index 686d0d0..db08765 100644
--- a/src/utils/DOMHelper.ts
+++ b/src/utils/DOMHelper.ts
@@ -28,7 +28,11 @@ function setBodyIndent(shouldShowGitako: boolean) {
   }
 }
 
-function $(selector: string, existCallback?: (element: Element) => any, otherwise?: () => any) {
+function $<R1 = never, R2 = never>(
+  selector: string,
+  existCallback?: (element: Element) => R1,
+  otherwise?: () => R2,
+): R1 | R2 | Element {
   const element = document.querySelector(selector)
   if (element) {
     return existCallback ? existCallback(element) : element
@@ -52,14 +56,14 @@ function getCurrentBranch() {
     '.repository-content > .file-navigation > .branch-select-menu > button'
   const branchNameFromButtonElement = $(
     selectedBranchButtonSelector,
-    (element: HTMLButtonElement) => element.title.trim()
+    (element: HTMLButtonElement) => element.title.trim(),
   )
   if (branchNameFromButtonElement) return branchNameFromButtonElement
 
   const selectedBranchSelector =
     '.select-menu.branch-select-menu .select-menu-modal .select-menu-list .select-menu-item.selected svg.select-menu-item-icon + span'
   const branchNameFromSelectElement = $(selectedBranchSelector, element =>
-    element.textContent.trim()
+    element.textContent.trim(),
   )
   if (branchNameFromSelectElement) return branchNameFromSelectElement
 }
@@ -299,7 +303,7 @@ function attachCopySnippet() {
           target.parentNode.insertBefore(clippy, target)
         }
       }
-    })
+    }),
   )
 }
 
diff --git a/src/utils/keyHelper.ts b/src/utils/keyHelper.ts
index e43b60d..b048c07 100644
--- a/src/utils/keyHelper.ts
+++ b/src/utils/keyHelper.ts
@@ -1,5 +1,3 @@
-import { KeyboardEvent } from 'react'
-
 const keyCodeArray = [
   ...'1234567890abcdefghijklmnopqrstuvwxyz'.split(''),
   ..."`[]\\;',./".split(''),
@@ -38,7 +36,7 @@ function parseKeyCode(code: string) {
   return code.toLowerCase().replace(/^control$/, 'ctrl')
 }
 
-function parseEvent(e: KeyboardEvent<HTMLInputElement>) {
+function parseEvent(e: KeyboardEvent | React.KeyboardEvent) {
   const { altKey: alt, shiftKey: shift, metaKey: meta, ctrlKey: ctrl } = e
   const code = parseKeyCode(e.key)
   const keys = { meta, ctrl, shift, alt, [code]: true }