diff --git a/packages/driver/src/config/jquery.ts b/packages/driver/src/config/jquery.ts
index 0b16e6f1c31..d998e6af709 100644
--- a/packages/driver/src/config/jquery.ts
+++ b/packages/driver/src/config/jquery.ts
@@ -1,11 +1,17 @@
-// @ts-nocheck
-
-import $ from 'jquery'
+import JQuery from 'jquery'
 import _ from 'lodash'
 
 import { scrollTo } from './jquery.scrollto'
 import $dom from '../dom'
 
+// Add missing types.
+interface ExtendedJQueryStatic extends JQueryStatic {
+  find: any
+  expr: JQuery.Selectors & { filters: any }
+}
+
+const $: ExtendedJQueryStatic = JQuery as any
+
 // force jquery to have the same visible
 // and hidden logic as cypress
 
diff --git a/packages/driver/src/cy/commands/actions/check.ts b/packages/driver/src/cy/commands/actions/check.ts
index 41dc231e50f..490bbd3559a 100644
--- a/packages/driver/src/cy/commands/actions/check.ts
+++ b/packages/driver/src/cy/commands/actions/check.ts
@@ -1,4 +1,3 @@
-// @ts-nocheck
 import _ from 'lodash'
 import Promise from 'bluebird'
 
@@ -7,7 +6,7 @@ import $utils from '../../../cypress/utils'
 import $errUtils from '../../../cypress/error_utils'
 import $elements from '../../../dom/elements'
 
-const checkOrUncheck = (Cypress, cy, type, subject, values = [], userOptions = {}) => {
+const checkOrUncheck = (Cypress, cy, type, subject, values: any[] = [], userOptions = {}) => {
   // we're not handling conversion of values to strings
   // in case we've received numbers
 
@@ -18,15 +17,15 @@ const checkOrUncheck = (Cypress, cy, type, subject, values = [], userOptions = {
     values = []
   } else {
     // make sure we're an array of values
-    values = [].concat(values)
+    values = ([] as any[]).concat(values)
   }
 
   // keep an array of subjects which
   // are potentially reduced down
   // to new filtered subjects
-  const matchingElements = []
+  const matchingElements: HTMLElement[] = []
 
-  const options = _.defaults({}, userOptions, {
+  const options: Record<string, any> = _.defaults({}, userOptions, {
     $el: subject,
     log: true,
     force: false,
@@ -75,7 +74,7 @@ const checkOrUncheck = (Cypress, cy, type, subject, values = [], userOptions = {
       matchingElements.push(el)
     }
 
-    const consoleProps = {
+    const consoleProps: Record<string, any> = {
       'Applied To': $dom.getElements($el),
       'Elements': $el.length,
     }
diff --git a/packages/driver/src/cy/commands/actions/trigger.ts b/packages/driver/src/cy/commands/actions/trigger.ts
index cdef7d59c65..1241cb4e64b 100644
--- a/packages/driver/src/cy/commands/actions/trigger.ts
+++ b/packages/driver/src/cy/commands/actions/trigger.ts
@@ -1,5 +1,3 @@
-// @ts-nocheck
-
 import _ from 'lodash'
 import Promise from 'bluebird'
 
@@ -59,7 +57,7 @@ export default (Commands, Cypress, cy, state, config) => {
 
       ({ options: userOptions, position, x, y } = $actionability.getPositionFromArguments(positionOrX, y, userOptions))
 
-      const options = _.defaults({}, userOptions, {
+      const options: Record<string, any> = _.defaults({}, userOptions, {
         log: true,
         $el: subject,
         bubbles: true,
diff --git a/packages/driver/src/cy/commands/actions/type.ts b/packages/driver/src/cy/commands/actions/type.ts
index 4e3e8a3a032..4ef46395b1c 100644
--- a/packages/driver/src/cy/commands/actions/type.ts
+++ b/packages/driver/src/cy/commands/actions/type.ts
@@ -1,4 +1,3 @@
-// @ts-nocheck
 import _ from 'lodash'
 import Promise from 'bluebird'
 
@@ -15,7 +14,11 @@ const debug = debugFn('cypress:driver:command:type')
 export default function (Commands, Cypress, cy, state, config) {
   const { keyboard } = cy.devices
 
-  function type (subject, chars, options = {}) {
+  // Note: These "change type of `any` to X" comments are written instead of changing them directly
+  //       because Cypress extends user-given options with Cypress internal options.
+  //       These comments will be removed after removing `// @ts-nocheck` comments in `packages/driver`.
+  // TODO: change the type of `any` to `Partial<Cypress.TypeOptions>`
+  function type (subject, chars, options: any = {}) {
     const userOptions = options
     let updateTable
 
@@ -366,7 +369,7 @@ export default function (Commands, Cypress, cy, state, config) {
             // Firefox sends a click event automatically.
             if (!Cypress.isBrowser('firefox')) {
               const ctor = $dom.getDocumentFromElement(el).defaultView?.PointerEvent
-              const event = new ctor('click')
+              const event = new ctor!('click')
 
               el.dispatchEvent(event)
             }
@@ -510,7 +513,8 @@ export default function (Commands, Cypress, cy, state, config) {
     })
   }
 
-  function clear (subject, options = {}) {
+  // TODO: change the type of `any` to `Partial<ClearOptions>`
+  function clear (subject, options: any = {}) {
     const userOptions = options
 
     options = _.defaults({}, userOptions, {
diff --git a/packages/driver/src/cy/commands/connectors.ts b/packages/driver/src/cy/commands/connectors.ts
index 730da1c3e4b..22dd18dfb5e 100644
--- a/packages/driver/src/cy/commands/connectors.ts
+++ b/packages/driver/src/cy/commands/connectors.ts
@@ -1,13 +1,11 @@
-// @ts-nocheck
-
 import _ from 'lodash'
 import Promise from 'bluebird'
 
 import $dom from '../../dom'
 import $utils from '../../cypress/utils'
-import $errUtils from '../../cypress/error_utils'
+import $errUtils, { CypressError } from '../../cypress/error_utils'
 
-const returnFalseIfThenable = (key, ...args) => {
+const returnFalseIfThenable = (key, ...args): boolean => {
   if ((key === 'then') && _.isFunction(args[0]) && _.isFunction(args[1])) {
     // https://github.com/cypress-io/cypress/issues/111
     // if we're inside of a promise then the promise lib will naturally
@@ -22,6 +20,8 @@ const returnFalseIfThenable = (key, ...args) => {
 
     return false
   }
+
+  return true
 }
 
 const primitiveToObject = (memo) => {
@@ -181,7 +181,7 @@ export default function (Commands, Cypress, cy, state) {
 
   const invokeFn = (subject, userOptionsOrStr, ...args) => {
     const userOptionsPassed = _.isObject(userOptionsOrStr) && !_.isFunction(userOptionsOrStr)
-    let userOptions = null
+    let userOptions: Record<string, any> | null = null
     let str = null
 
     if (!userOptionsPassed) {
@@ -219,7 +219,7 @@ export default function (Commands, Cypress, cy, state) {
 
     const message = getMessage()
 
-    let traversalErr = null
+    let traversalErr: CypressError | null = null
 
     // copy userOptions because _log is added below.
     const options = _.extend({}, userOptions)
@@ -568,7 +568,7 @@ export default function (Commands, Cypress, cy, state) {
           return ret
         }
 
-        return thenFn(el, userOptions, callback, state)
+        return thenFn(el, userOptions, callback)
       }
 
       // generate a real array since bluebird is finicky and
@@ -586,9 +586,9 @@ export default function (Commands, Cypress, cy, state) {
   // cy.resolve + cy.wrap are upgraded to handle
   // promises
   Commands.addAll({ prevSubject: 'optional' }, {
-    then () {
+    then (subject, userOptions, fn) {
       // eslint-disable-next-line prefer-rest-params
-      return thenFn.apply(this, arguments)
+      return thenFn.apply(this, [subject, userOptions, fn])
     },
   })
 
diff --git a/packages/driver/src/cy/commands/cookies.ts b/packages/driver/src/cy/commands/cookies.ts
index 3c8f09e36de..9002763dc0d 100644
--- a/packages/driver/src/cy/commands/cookies.ts
+++ b/packages/driver/src/cy/commands/cookies.ts
@@ -1,5 +1,3 @@
-// @ts-nocheck
-
 import _ from 'lodash'
 import Promise from 'bluebird'
 
@@ -110,7 +108,7 @@ export default function (Commands, Cypress, cy, state, config) {
     })
   }
 
-  const getAndClear = (log, timeout, options = {}) => {
+  const getAndClear = (log?, timeout?, options = {}) => {
     return automateCookies('get:cookies', options, log, timeout)
     .then((resp) => {
     // bail early if we got no cookies!
@@ -166,7 +164,8 @@ export default function (Commands, Cypress, cy, state, config) {
   })
 
   return Commands.addAll({
-    getCookie (name, options = {}) {
+    // TODO: change the type of `any` to `Partial<Cypress.Loggable & Cypress.Timeoutable>`
+    getCookie (name, options: any = {}) {
       const userOptions = options
 
       options = _.defaults({}, userOptions, {
@@ -212,7 +211,8 @@ export default function (Commands, Cypress, cy, state, config) {
       .catch(handleBackendError('getCookie', 'reading the requested cookie from', onFail))
     },
 
-    getCookies (options = {}) {
+    // TODO: change the type of `any` to `Partial<Cypress.Loggable & Cypress.Timeoutable>`
+    getCookies (options: any = {}) {
       const userOptions = options
 
       options = _.defaults({}, userOptions, {
@@ -250,7 +250,8 @@ export default function (Commands, Cypress, cy, state, config) {
       .catch(handleBackendError('getCookies', 'reading cookies from', options._log))
     },
 
-    setCookie (name, value, options = {}) {
+    // TODO: change the type of `any` to `Partial<Cypress.SetCookieOptions>`
+    setCookie (name, value, options: any = {}) {
       const userOptions = options
 
       options = _.defaults({}, userOptions, {
@@ -331,7 +332,8 @@ export default function (Commands, Cypress, cy, state, config) {
       }).catch(handleBackendError('setCookie', 'setting the requested cookie in', onFail))
     },
 
-    clearCookie (name, options = {}) {
+    // TODO: change the type of `any` to `Partial<Cypress.Loggable & Cypress.Timeoutable>`
+    clearCookie (name, options: any = {}) {
       const userOptions = options
 
       options = _.defaults({}, userOptions, {
@@ -380,7 +382,8 @@ export default function (Commands, Cypress, cy, state, config) {
       .catch(handleBackendError('clearCookie', 'clearing the requested cookie in', onFail))
     },
 
-    clearCookies (options = {}) {
+    // TODO: change the type of `any` to `Partial<Cypress.Loggable & Cypress.Timeoutable>`
+    clearCookies (options: any = {}) {
       const userOptions = options
 
       options = _.defaults({}, userOptions, {
diff --git a/packages/driver/src/cy/commands/exec.ts b/packages/driver/src/cy/commands/exec.ts
index 9727db3b448..d6114590579 100644
--- a/packages/driver/src/cy/commands/exec.ts
+++ b/packages/driver/src/cy/commands/exec.ts
@@ -1,5 +1,3 @@
-// @ts-nocheck
-
 import _ from 'lodash'
 import Promise from 'bluebird'
 
@@ -7,7 +5,8 @@ import $errUtils from '../../cypress/error_utils'
 
 export default (Commands, Cypress, cy) => {
   Commands.addAll({
-    exec (cmd, options = {}) {
+    // TODO: change the type of `any` to `Partical<Cypress.ExecOptions>`
+    exec (cmd, options: any = {}) {
       const userOptions = options
 
       options = _.defaults({}, userOptions, {
diff --git a/packages/driver/src/cy/commands/files.ts b/packages/driver/src/cy/commands/files.ts
index d88b1279e73..a87a9f9ee25 100644
--- a/packages/driver/src/cy/commands/files.ts
+++ b/packages/driver/src/cy/commands/files.ts
@@ -1,4 +1,3 @@
-// @ts-nocheck
 import _ from 'lodash'
 import { basename } from 'path'
 
@@ -6,7 +5,8 @@ import $errUtils from '../../cypress/error_utils'
 
 export default (Commands, Cypress, cy, state) => {
   Commands.addAll({
-    readFile (file, encoding, options = {}) {
+    // TODO: change the type of `any` to `Partial<Cypress.Loggable & Cypress.Timeoutable>`
+    readFile (file, encoding, options: any = {}) {
       let userOptions = options
 
       if (_.isObject(encoding)) {
@@ -109,7 +109,8 @@ export default (Commands, Cypress, cy, state) => {
       return verifyAssertions()
     },
 
-    writeFile (fileName, contents, encoding, options = {}) {
+    // TODO: change the type of `any` to `Partial<Cypress.WriteFileOPtions & Cypress.Timeoutable>`
+    writeFile (fileName, contents, encoding, options: any = {}) {
       let userOptions = options
 
       if (_.isObject(encoding)) {
diff --git a/packages/driver/src/cy/commands/fixtures.ts b/packages/driver/src/cy/commands/fixtures.ts
index c4a84b40e44..9d142df77bb 100644
--- a/packages/driver/src/cy/commands/fixtures.ts
+++ b/packages/driver/src/cy/commands/fixtures.ts
@@ -1,5 +1,3 @@
-// @ts-nocheck
-
 import _ from 'lodash'
 import Promise from 'bluebird'
 import { basename } from 'path'
@@ -44,7 +42,7 @@ export default (Commands, Cypress, cy, state, config) => {
         return Promise.resolve(clone(resp))
       }
 
-      let options = {}
+      let options: Record<string, any> = {}
 
       if (_.isObject(args[0])) {
         options = args[0]
diff --git a/packages/driver/src/cy/commands/location.ts b/packages/driver/src/cy/commands/location.ts
index d0bbf37ab00..837d39b8a3d 100644
--- a/packages/driver/src/cy/commands/location.ts
+++ b/packages/driver/src/cy/commands/location.ts
@@ -1,5 +1,3 @@
-// @ts-nocheck
-
 import _ from 'lodash'
 import Promise from 'bluebird'
 
@@ -8,7 +6,8 @@ const { throwErrByPath } = $errUtils
 
 export default (Commands, Cypress, cy) => {
   Commands.addAll({
-    url (options = {}) {
+    // TODO: change the type of `any` to `Partial<Cypress.UrlOptions>`
+    url (options: any = {}) {
       const userOptions = options
 
       options = _.defaults({}, userOptions, { log: true })
@@ -39,7 +38,8 @@ export default (Commands, Cypress, cy) => {
       return resolveHref()
     },
 
-    hash (options = {}) {
+    // TODO: change the type of `any` to `Partial<Cypress.Loggable & Cypress.Timeoutable>`
+    hash (options: any = {}) {
       const userOptions = options
 
       options = _.defaults({}, userOptions, { log: true })
diff --git a/packages/driver/src/cy/commands/misc.ts b/packages/driver/src/cy/commands/misc.ts
index c0594562bed..5a0db7a0f09 100644
--- a/packages/driver/src/cy/commands/misc.ts
+++ b/packages/driver/src/cy/commands/misc.ts
@@ -1,4 +1,3 @@
-// @ts-nocheck
 import _ from 'lodash'
 import Promise from 'bluebird'
 
@@ -50,7 +49,8 @@ export default (Commands, Cypress, cy, state) => {
       return null
     },
 
-    wrap (arg, options = {}) {
+    // TODO: change the type of `any` to `Partial<Cypress.Loggable & Cypress.Timeoutable>`
+    wrap (arg, options: any = {}) {
       const userOptions = options
 
       options = _.defaults({}, userOptions, {
diff --git a/packages/driver/src/cy/commands/navigation.ts b/packages/driver/src/cy/commands/navigation.ts
index 07f184ba04e..c3afb98731c 100644
--- a/packages/driver/src/cy/commands/navigation.ts
+++ b/packages/driver/src/cy/commands/navigation.ts
@@ -1,5 +1,3 @@
-// @ts-nocheck
-/* global cy, Cypress */
 import _ from 'lodash'
 import whatIsCircular from '@cypress/what-is-circular'
 import UrlParse from 'url-parse'
@@ -15,10 +13,10 @@ import debugFn from 'debug'
 const debug = debugFn('cypress:driver:navigation')
 
 let id = null
-let previousDomainVisited = null
-let hasVisitedAboutBlank = null
-let currentlyVisitingAboutBlank = null
-let knownCommandCausedInstability = null
+let previousDomainVisited: boolean = false
+let hasVisitedAboutBlank: boolean = false
+let currentlyVisitingAboutBlank: boolean = false
+let knownCommandCausedInstability: boolean = false
 
 const REQUEST_URL_OPTS = 'auth failOnStatusCode retryOnNetworkFailure retryOnStatusCodeFailure retryIntervals method body headers'
 .split(' ')
@@ -27,7 +25,7 @@ const VISIT_OPTS = 'url log onBeforeLoad onLoad timeout requestTimeout'
 .split(' ')
 .concat(REQUEST_URL_OPTS)
 
-const reset = (test = {}) => {
+const reset = (test: any = {}) => {
   knownCommandCausedInstability = false
 
   // continuously reset this
@@ -62,7 +60,7 @@ const timedOutWaitingForPageLoad = (ms, log) => {
 }
 
 const cannotVisitDifferentOrigin = (origin, previousUrlVisited, remoteUrl, existingUrl, log) => {
-  const differences = []
+  const differences: string[] = []
 
   if (remoteUrl.protocol !== existingUrl.protocol) {
     differences.push('protocol')
@@ -171,7 +169,7 @@ const navigationChanged = (Cypress, cy, state, source, arg) => {
     end: true,
     snapshot: true,
     consoleProps () {
-      const obj = {
+      const obj: Record<string, any> = {
         'New Url': url,
       }
 
@@ -265,7 +263,7 @@ const stabilityChanged = (Cypress, state, config, stable) => {
     return
   }
 
-  const options = {}
+  const options: Record<string, any> = {}
 
   _.defaults(options, {
     timeout: config('pageLoadTimeout'),
@@ -404,6 +402,14 @@ const normalizeTimeoutOptions = (options) => {
   .value()
 }
 
+type NotOkResponseError = Error & {
+  gotResponse: boolean
+}
+
+type InvalidContentTypeError = Error & {
+  invalidContentType: boolean
+}
+
 export default (Commands, Cypress, cy, state, config) => {
   reset()
 
@@ -420,7 +426,7 @@ export default (Commands, Cypress, cy, state, config) => {
   Cypress.on('stability:changed', (bool, event) => {
     // only send up page loading events when we're
     // not stable!
-    stabilityChanged(Cypress, state, config, bool, event)
+    stabilityChanged(Cypress, state, config, bool)
   })
 
   Cypress.on('navigation:changed', (source, arg) => {
@@ -445,11 +451,11 @@ export default (Commands, Cypress, cy, state, config) => {
       url,
       normalizeTimeoutOptions(options),
     )
-    .then((resp = {}) => {
+    .then((resp: any = {}) => {
       if (!resp.isOkStatusCode) {
         // if we didn't even get an OK response
         // then immediately die
-        const err = new Error
+        const err: NotOkResponseError = new Error as any
 
         err.gotResponse = true
         _.extend(err, resp)
@@ -459,7 +465,7 @@ export default (Commands, Cypress, cy, state, config) => {
 
       if (!resp.isHtml) {
         // throw invalid contentType error
-        const err = new Error
+        const err: InvalidContentTypeError = new Error as any
 
         err.invalidContentType = true
         _.extend(err, resp)
@@ -525,7 +531,7 @@ export default (Commands, Cypress, cy, state, config) => {
       // clear the current timeout
       cy.clearTimeout('reload')
 
-      let cleanup = null
+      let cleanup: (() => any) | null = null
       const options = _.defaults({}, userOptions, {
         log: true,
         timeout: config('pageLoadTimeout'),
@@ -579,7 +585,7 @@ export default (Commands, Cypress, cy, state, config) => {
     },
 
     go (numberOrString, userOptions = {}) {
-      const options = _.defaults({}, userOptions, {
+      const options: Record<string, any> = _.defaults({}, userOptions, {
         log: true,
         timeout: config('pageLoadTimeout'),
       })
@@ -595,7 +601,7 @@ export default (Commands, Cypress, cy, state, config) => {
           $errUtils.throwErrByPath('go.invalid_number', { onFail: options._log })
         }
 
-        let cleanup = null
+        let cleanup: (() => any) | null = null
 
         if (options._log) {
           options._log.snapshot('before', { next: 'after' })
@@ -669,7 +675,7 @@ export default (Commands, Cypress, cy, state, config) => {
           case 'forward': return goNumber(1)
           case 'back': return goNumber(-1)
           default:
-            $errUtils.throwErrByPath('go.invalid_direction', {
+            return $errUtils.throwErrByPath('go.invalid_direction', {
               onFail: options._log,
               args: { str },
             })
@@ -684,10 +690,11 @@ export default (Commands, Cypress, cy, state, config) => {
         return goString(numberOrString)
       }
 
-      $errUtils.throwErrByPath('go.invalid_argument', { onFail: options._log })
+      return $errUtils.throwErrByPath('go.invalid_argument', { onFail: options._log })
     },
 
-    visit (url, options = {}) {
+    // TODO: Change the type of `any` to `Partial<Cypress.VisitOptions>`.
+    visit (url, options: any = {}) {
       if (options.url && url) {
         $errUtils.throwErrByPath('visit.no_duplicate_url', { args: { optionsUrl: options.url, url } })
       }
@@ -778,7 +785,7 @@ export default (Commands, Cypress, cy, state, config) => {
         url = $Location.mergeUrlWithParams(url, qs)
       }
 
-      let cleanup = null
+      let cleanup: (() => any) | null = null
 
       // clear the current timeout
       cy.clearTimeout('visit')
@@ -801,7 +808,7 @@ export default (Commands, Cypress, cy, state, config) => {
               })
 
               options.onBeforeLoad?.call(runnable.ctx, contentWindow)
-            } catch (err) {
+            } catch (err: any) {
               err.isCallbackError = true
               onBeforeLoadError = err
             }
@@ -847,7 +854,10 @@ export default (Commands, Cypress, cy, state, config) => {
         })
       }
 
-      const onLoad = ({ runOnLoadCallback, totalTime }) => {
+      const onLoad = ({ runOnLoadCallback, totalTime }: {
+        runOnLoadCallback?: boolean
+        totalTime?: number
+      }) => {
         // reset window on load
         win = state('window')
 
@@ -855,7 +865,7 @@ export default (Commands, Cypress, cy, state, config) => {
         if (runOnLoadCallback !== false) {
           try {
             options.onLoad?.call(runnable.ctx, win)
-          } catch (err) {
+          } catch (err: any) {
             // mark these as user callback errors, so they're treated differently
             // than Node.js errors when caught below
             err.isCallbackError = true
@@ -930,7 +940,9 @@ export default (Commands, Cypress, cy, state, config) => {
           }
 
           return changeIframeSrc(remote.href, 'hashchange')
-          .then(onLoad)
+          .then(() => {
+            return onLoad({})
+          })
         }
 
         if (existingHash) {
@@ -945,7 +957,7 @@ export default (Commands, Cypress, cy, state, config) => {
         }
 
         return requestUrl(url, options)
-        .then((resp = {}) => {
+        .then((resp: any = {}) => {
           let { url, originalUrl, cookies, redirects, filePath } = resp
 
           // reapply the existing hash
@@ -1000,7 +1012,7 @@ export default (Commands, Cypress, cy, state, config) => {
           // tell our backend we're changing domains
           // TODO: add in other things we want to preserve
           // state for like scrollTop
-          let s = {
+          let s: Record<string, any> = {
             currentId: id,
             tests: Cypress.runner.getTestsState(),
             startTime: Cypress.runner.getStartTime(),
diff --git a/packages/driver/src/cypress/browser.ts b/packages/driver/src/cypress/browser.ts
index 0a3c3678cd3..28352d4a4e2 100644
--- a/packages/driver/src/cypress/browser.ts
+++ b/packages/driver/src/cypress/browser.ts
@@ -1,4 +1,3 @@
-// @ts-nocheck
 import _ from 'lodash'
 import $utils from './utils'
 import $errUtils from './error_utils'
@@ -36,12 +35,16 @@ const _isBrowser = (browser, matcher, errPrefix) => {
   }
 }
 
-const isBrowser = (config, obj = '', errPrefix = '`Cypress.isBrowser()`') => {
+// TODO: change the type of `any` to `IsBrowserMatcher`
+const isBrowser = (config, obj: any = '', errPrefix: string = '`Cypress.isBrowser()`') => {
   return _
   .chain(obj)
   .concat([])
   .map((matcher) => _isBrowser(config.browser, matcher, errPrefix))
-  .reduce((a, b) => {
+  .reduce((
+    a: null | { isMatch: boolean, exclusive: boolean },
+    b: { isMatch: boolean, exclusive: boolean },
+  ) => {
     if (!a) return b
 
     if (a.exclusive && b.exclusive) {
diff --git a/packages/driver/src/cypress/chai_jquery.ts b/packages/driver/src/cypress/chai_jquery.ts
index f4f7f675c32..23a13ada956 100644
--- a/packages/driver/src/cypress/chai_jquery.ts
+++ b/packages/driver/src/cypress/chai_jquery.ts
@@ -1,4 +1,3 @@
-// @ts-nocheck
 import _ from 'lodash'
 import $ from 'jquery'
 import $dom from '../dom'
@@ -33,7 +32,12 @@ const maybeCastNumberToString = (num) => {
   return _.isFinite(num) ? `${num}` : num
 }
 
-export const $chaiJquery = (chai, chaiUtils, callbacks = {}) => {
+interface Callbacks {
+  onInvalid: (method, obj) => void
+  onError: (err, method, obj, negated) => void
+}
+
+export const $chaiJquery = (chai, chaiUtils, callbacks: Callbacks) => {
   const { inspect, flag } = chaiUtils
 
   const assertDom = (ctx, method, ...args) => {
diff --git a/packages/driver/src/cypress/commands.ts b/packages/driver/src/cypress/commands.ts
index 574b62a6ad7..0384c887d45 100644
--- a/packages/driver/src/cypress/commands.ts
+++ b/packages/driver/src/cypress/commands.ts
@@ -1,5 +1,3 @@
-// @ts-nocheck
-
 import _ from 'lodash'
 
 import $errUtils from './error_utils'
@@ -9,6 +7,8 @@ import { allCommands } from '../cy/commands'
 import { addCommand } from '../cy/net-stubbing'
 
 const builtInCommands = [
+  // `default` is necessary if a file uses `export default` syntax.
+  // @ts-ignore
   ..._.toArray(allCommands).map((c) => c.default || c),
   addCommand,
 ]
@@ -74,7 +74,7 @@ export default {
       const overridden = _.clone(original)
 
       overridden.fn = function (...args) {
-        args = [].concat(originalFn, args)
+        args = ([] as any).concat(originalFn, args)
 
         return fn.apply(this, args)
       }
diff --git a/packages/driver/src/cypress/cookies.ts b/packages/driver/src/cypress/cookies.ts
index c5bf498a5cb..28d15317cc2 100644
--- a/packages/driver/src/cypress/cookies.ts
+++ b/packages/driver/src/cypress/cookies.ts
@@ -1,5 +1,3 @@
-// @ts-nocheck
-
 import _ from 'lodash'
 import Cookies from 'js-cookie'
 
@@ -10,13 +8,13 @@ let isDebuggingVerbose = false
 
 const preserved = {}
 
-const defaults = {
+const defaults: any = {
   preserve: null,
 }
 
 const warnOnWhitelistRenamed = (obj, type) => {
   if (obj.whitelist) {
-    return $errUtils.throwErrByPath('cookies.whitelist_renamed', { args: { type } })
+    $errUtils.throwErrByPath('cookies.whitelist_renamed', { args: { type } })
   }
 }
 
@@ -53,10 +51,12 @@ export const $Cookies = (namespace, domain) => {
     if (preserved[name]) {
       return delete preserved[name]
     }
+
+    return false
   }
 
   const API = {
-    debug (bool = true, options = {}) {
+    debug (bool = true, options: any = {}) {
       _.defaults(options, {
         verbose: true,
       })
@@ -82,7 +82,7 @@ export const $Cookies = (namespace, domain) => {
       return console[m].apply(console, args)
     },
 
-    getClearableCookies (cookies = []) {
+    getClearableCookies (cookies: any[] = []) {
       return _.filter(cookies, (cookie) => {
         return !isAllowed(cookie) && !removePreserved(cookie.name)
       })
diff --git a/packages/driver/src/cypress/error_utils.ts b/packages/driver/src/cypress/error_utils.ts
index 0645822e71f..7d7cf105efd 100644
--- a/packages/driver/src/cypress/error_utils.ts
+++ b/packages/driver/src/cypress/error_utils.ts
@@ -1,5 +1,3 @@
-// @ts-nocheck
-
 // See: ./errorScenarios.md for details about error messages and stack traces
 
 import _ from 'lodash'
@@ -7,7 +5,7 @@ import chai from 'chai'
 
 import $dom from '../dom'
 import $utils from './utils'
-import $stackUtils from './stack_utils'
+import $stackUtils, { StackAndCodeFrameIndex } from './stack_utils'
 import $errorMessages from './error_messages'
 
 const ERROR_PROPS = 'message type name stack sourceMappedStack parsedStack fileName lineNumber columnNumber host uncaught actual expected showDiff isPending docsUrl codeFrame'.split(' ')
@@ -17,9 +15,9 @@ const crossOriginScriptRe = /^script error/i
 
 if (!Error.captureStackTrace) {
   Error.captureStackTrace = (err, fn) => {
-    const stack = (new Error()).stack
+    const stack = (new Error()).stack;
 
-    err.stack = $stackUtils.stackWithLinesDroppedFromMarker(stack, fn.name)
+    (err as Error).stack = $stackUtils.stackWithLinesDroppedFromMarker(stack, fn?.name)
   }
 }
 
@@ -63,15 +61,15 @@ const wrapErr = (err) => {
   return $utils.reduceProps(err, ERROR_PROPS)
 }
 
-const isAssertionErr = (err = {}) => {
+const isAssertionErr = (err: Error) => {
   return err.name === 'AssertionError'
 }
 
-const isChaiValidationErr = (err = {}) => {
+const isChaiValidationErr = (err: Error) => {
   return _.startsWith(err.message, 'Invalid Chai property')
 }
 
-const isCypressErr = (err = {}) => {
+const isCypressErr = (err: Error): boolean => {
   return err.name === 'CypressError'
 }
 
@@ -79,7 +77,7 @@ const isSpecError = (spec, err) => {
   return _.includes(err.stack, spec.relative)
 }
 
-const mergeErrProps = (origErr: Error, ...newProps) => {
+const mergeErrProps = (origErr: Error, ...newProps): Error => {
   return _.extend(origErr, ...newProps)
 }
 
@@ -197,7 +195,7 @@ const makeErrFromObj = (obj) => {
   return err2
 }
 
-const throwErr = (err, options = {}) => {
+const makeErrFromErr = (err, options: any = {}) => {
   if (_.isString(err)) {
     err = cypressErr({ message: err })
   }
@@ -205,12 +203,12 @@ const throwErr = (err, options = {}) => {
   let { onFail, errProps } = options
 
   // assume onFail is a command if
-  //# onFail is present and isn't a function
+  // onFail is present and isn't a function
   if (onFail && !_.isFunction(onFail)) {
     const command = onFail
 
-    //# redefine onFail and automatically
-    //# hook this into our command
+    // redefine onFail and automatically
+    // hook this into our command
     onFail = (err) => {
       return command.error(err)
     }
@@ -224,10 +222,14 @@ const throwErr = (err, options = {}) => {
     _.extend(err, errProps)
   }
 
-  throw err
+  return err
+}
+
+const throwErr = (err, options: any = {}): never => {
+  throw makeErrFromErr(err, options)
 }
 
-const throwErrByPath = (errPath, options = {}) => {
+const throwErrByPath = (errPath, options: any = {}): never => {
   const err = errByPath(errPath, options.args)
 
   if (options.stack) {
@@ -237,15 +239,16 @@ const throwErrByPath = (errPath, options = {}) => {
     Error.captureStackTrace(err, throwErrByPath)
   }
 
-  throwErr(err, options)
+  throw makeErrFromErr(err, options)
 }
 
-const warnByPath = (errPath, options = {}) => {
+const warnByPath = (errPath, options: any = {}) => {
   const errObj = errByPath(errPath, options.args)
   let err = errObj.message
+  const docsUrl = (errObj as CypressError).docsUrl
 
-  if (errObj.docsUrl) {
-    err += `\n\n${errObj.docsUrl}`
+  if (docsUrl) {
+    err += `\n\n${docsUrl}`
   }
 
   $utils.warning(err)
@@ -266,6 +269,7 @@ export class InternalCypressError extends Error {
 export class CypressError extends Error {
   docsUrl?: string
   retry?: boolean
+  userInvocationStack?: any
 
   constructor (message) {
     super(message)
@@ -297,10 +301,10 @@ const internalErr = (err): InternalCypressError => {
 const cypressErr = (err): CypressError => {
   const newErr = new CypressError(err.message)
 
-  return mergeErrProps(newErr, err)
+  return mergeErrProps(newErr, err) as CypressError
 }
 
-const cypressErrByPath = (errPath, options = {}) => {
+const cypressErrByPath = (errPath, options: any = {}) => {
   const errObj = errByPath(errPath, options.args)
 
   return cypressErr(errObj)
@@ -376,7 +380,7 @@ const createUncaughtException = ({ frameType, handlerType, state, err }) => {
   let uncaughtErr = errByPath(errPath, {
     errMsg: err.message,
     promiseAddendum: handlerType === 'unhandledrejection' ? ' It was caused by an unhandled promise rejection.' : '',
-  })
+  }) as CypressError
 
   modifyErrMsg(err, uncaughtErr.message, () => uncaughtErr.message)
 
@@ -394,7 +398,7 @@ const createUncaughtException = ({ frameType, handlerType, state, err }) => {
 // stacks from command failures and assertion failures have the right message
 // but the stack points to cypress internals. here we replace the internal
 // cypress stack with the invocation stack, which points to the user's code
-const stackAndCodeFrameIndex = (err, userInvocationStack) => {
+const stackAndCodeFrameIndex = (err, userInvocationStack): StackAndCodeFrameIndex => {
   if (!userInvocationStack) return { stack: err.stack }
 
   if (isCypressErr(err) || isChaiValidationErr(err)) {
@@ -427,7 +431,7 @@ const enhanceStack = ({ err, userInvocationStack, projectRoot }) => {
 
 // all errors flow through this function before they're finally thrown
 // or used to reject promises
-const processErr = (errObj = {}, config) => {
+const processErr = (errObj: CypressError, config) => {
   let docsUrl = errObj.docsUrl
 
   if (config('isInteractive') || !docsUrl) {
@@ -482,7 +486,7 @@ const errorFromErrorEvent = (event): ErrorFromErrorEvent => {
   // reset the message on a cross origin script error
   // since no details are accessible
   if (crossOriginScriptRe.test(message)) {
-    const crossOriginErr = errByPath('uncaught.cross_origin_script')
+    const crossOriginErr = errByPath('uncaught.cross_origin_script') as CypressError
 
     message = crossOriginErr.message
     docsUrl = crossOriginErr.docsUrl
@@ -490,9 +494,9 @@ const errorFromErrorEvent = (event): ErrorFromErrorEvent => {
 
   // it's possible the error was thrown as a string (throw 'some error')
   // so create it in the case it's not already an object
-  const err = _.isObject(error) ? error : convertErrorEventPropertiesToObject({
+  const err = (_.isObject(error) ? error : convertErrorEventPropertiesToObject({
     message, filename, lineno, colno,
-  })
+  })) as CypressError
 
   err.docsUrl = docsUrl
 
diff --git a/packages/driver/src/cypress/location.ts b/packages/driver/src/cypress/location.ts
index 661a445f056..96837afd3b4 100644
--- a/packages/driver/src/cypress/location.ts
+++ b/packages/driver/src/cypress/location.ts
@@ -1,4 +1,3 @@
-// @ts-nocheck
 // TODO:
 // 1. test these method implementations using encoded characters
 // look at the spec to figure out whether we SHOULD be decoding them
@@ -18,6 +17,8 @@ const reLocalHost = /^(localhost|0\.0\.0\.0|127\.0\.0\.1)/
 const reQueryParam = /\?[^/]+/
 
 export class $Location {
+  remote: UrlParse
+
   constructor (remote) {
     this.remote = new UrlParse(remote)
   }
@@ -38,6 +39,8 @@ export class $Location {
         password,
       }
     }
+
+    return
   }
 
   getHash () {
diff --git a/packages/driver/src/cypress/stack_utils.ts b/packages/driver/src/cypress/stack_utils.ts
index 0a3d2a188d3..a3f3c12ee6e 100644
--- a/packages/driver/src/cypress/stack_utils.ts
+++ b/packages/driver/src/cypress/stack_utils.ts
@@ -66,7 +66,12 @@ const stackWithReplacementMarkerLineRemoved = (stack) => {
   })
 }
 
-const stackWithUserInvocationStackSpliced = (err, userInvocationStack) => {
+export type StackAndCodeFrameIndex = {
+  stack: string
+  index?: number
+}
+
+const stackWithUserInvocationStackSpliced = (err, userInvocationStack): StackAndCodeFrameIndex => {
   const stack = _.trim(err.stack, '\n') // trim newlines from end
   const [messageLines, stackLines] = splitStack(stack)
   const userInvocationStackWithoutMessage = stackWithoutMessage(userInvocationStack)
diff --git a/packages/driver/src/cypress/utils.ts b/packages/driver/src/cypress/utils.ts
index 9718338887d..9b83e5c82f8 100644
--- a/packages/driver/src/cypress/utils.ts
+++ b/packages/driver/src/cypress/utils.ts
@@ -98,7 +98,7 @@ export default {
     throw new Error(`The switch/case value: '${value}' did not match any cases: ${keys.join(', ')}.`)
   },
 
-  reduceProps (obj, props = []) {
+  reduceProps (obj, props: string[] = []) {
     if (!obj) {
       return null
     }
@@ -355,7 +355,7 @@ export default {
 
   // normalize more than {maxNewLines} new lines into
   // exactly {replacementNumLines} new lines
-  normalizeNewLines (str, maxNewLines, replacementNumLines) {
+  normalizeNewLines (str, maxNewLines, replacementNumLines?) {
     const moreThanMaxNewLinesRe = new RegExp(`\\n{${maxNewLines},}`)
     const replacementWithNumLines = replacementNumLines ?? maxNewLines