diff --git a/projects/plugins/jetpack/_inc/client/components/global-notices/state/notices/actions.js b/projects/plugins/jetpack/_inc/client/components/global-notices/state/notices/actions.js
index ac29f39ac2a9..fcc6ae1e679f 100644
--- a/projects/plugins/jetpack/_inc/client/components/global-notices/state/notices/actions.js
+++ b/projects/plugins/jetpack/_inc/client/components/global-notices/state/notices/actions.js
@@ -1,6 +1,12 @@
 import { uniqueId } from 'lodash';
 import { NEW_NOTICE, REMOVE_NOTICE } from '../action-types';
 
+/**
+ * Creates a remove notice action.
+ *
+ * @param {string} noticeId - Notice ID.
+ * @return {object} Action object.
+ */
 export function removeNotice( noticeId ) {
 	return {
 		noticeId: noticeId,
@@ -8,6 +14,14 @@ export function removeNotice( noticeId ) {
 	};
 }
 
+/**
+ * Creates a new notice action.
+ *
+ * @param {string} status  - Notice status.
+ * @param {string} text    - Notice text.
+ * @param {object} options - Notice options.
+ * @return {object} Action object.
+ */
 export function createNotice( status, text, options = {} ) {
 	const notice = {
 		noticeId: options.id || uniqueId(),
diff --git a/projects/plugins/jetpack/_inc/client/components/global-notices/state/notices/reducer.js b/projects/plugins/jetpack/_inc/client/components/global-notices/state/notices/reducer.js
index 3f7d3b491d81..0d9ee8531559 100644
--- a/projects/plugins/jetpack/_inc/client/components/global-notices/state/notices/reducer.js
+++ b/projects/plugins/jetpack/_inc/client/components/global-notices/state/notices/reducer.js
@@ -1,6 +1,13 @@
 import { combineReducers } from 'redux';
 import { NEW_NOTICE, REMOVE_NOTICE } from '../action-types';
 
+/**
+ * Reducer for global notices.
+ *
+ * @param {Array}  state  - Current state.
+ * @param {object} action - Action object.
+ * @return {Array} Updated state.
+ */
 export function globalNotices( state = [], action ) {
 	switch ( action.type ) {
 		case NEW_NOTICE:
diff --git a/projects/plugins/jetpack/_inc/client/components/modal/index.jsx b/projects/plugins/jetpack/_inc/client/components/modal/index.jsx
index 7bd0f977893e..45dd4122c0ee 100644
--- a/projects/plugins/jetpack/_inc/client/components/modal/index.jsx
+++ b/projects/plugins/jetpack/_inc/client/components/modal/index.jsx
@@ -17,10 +17,16 @@ let preventCloseFlag = false;
 
 import './style.scss';
 
+/**
+ * Prevents any modals from closing until {@link allowClose} is called.
+ */
 function preventClose() {
 	preventCloseFlag = true;
 }
 
+/**
+ * Allows modals to close again after {@link preventClose} was called.
+ */
 function allowClose() {
 	preventCloseFlag = false;
 }
diff --git a/projects/plugins/jetpack/_inc/client/components/popover/util.js b/projects/plugins/jetpack/_inc/client/components/popover/util.js
index 6e5ff3e76ba4..b88f928b18bb 100644
--- a/projects/plugins/jetpack/_inc/client/components/popover/util.js
+++ b/projects/plugins/jetpack/_inc/client/components/popover/util.js
@@ -7,6 +7,12 @@ import debugFactory from 'debug';
 const debug = debugFactory( 'calypso:popover:util' );
 
 // inspired by https://github.com/jkroso/viewport
+
+/**
+ * Updates and returns the current viewport dimensions.
+ *
+ * @return {object} Viewport object with top, left, width, height, right, and bottom.
+ */
 function updateViewport() {
 	const viewport = {};
 	viewport.top = window.scrollY;
@@ -38,6 +44,9 @@ const adjacent = {
 
 let viewport = updateViewport();
 
+/**
+ * Updates the cached viewport on window resize or scroll.
+ */
 function onViewportChange() {
 	viewport = updateViewport();
 }
@@ -95,6 +104,13 @@ const suggested = ( pos, el, target ) => {
 	return chooseSecondary( primary, pos1, el, target, w, h ) || pos;
 };
 
+/**
+ * Chooses the primary popover position based on available room.
+ *
+ * @param {string} prefered - Preferred position.
+ * @param {object} room     - Available room in each direction.
+ * @return {string|undefined} Best primary position.
+ */
 function choosePrimary( prefered, room ) {
 	// top, bottom, left, right in order of preference
 	const order = [
@@ -125,6 +141,17 @@ function choosePrimary( prefered, room ) {
 	return bestPos;
 }
 
+/**
+ * Chooses the secondary popover position based on visible area.
+ *
+ * @param {string}      primary  - Primary position.
+ * @param {string|null} prefered - Preferred secondary position.
+ * @param {HTMLElement} el       - Tip element.
+ * @param {HTMLElement} target   - Target element.
+ * @param {number}      w        - Tip width.
+ * @param {number}      h        - Tip height.
+ * @return {string|undefined} Best position string.
+ */
 function chooseSecondary( primary, prefered, el, target, w, h ) {
 	// top, top left, top right in order of preference
 	const order = prefered
@@ -170,6 +197,14 @@ function chooseSecondary( primary, prefered, el, target, w, h ) {
 	return bestPos;
 }
 
+/**
+ * Calculates the offset for a popover position.
+ *
+ * @param {string}      pos    - Position string.
+ * @param {HTMLElement} el     - Tip element.
+ * @param {HTMLElement} target - Target element.
+ * @return {object} Offset with top and left properties.
+ */
 function offset( pos, el, target ) {
 	const pad = 15;
 	const tipRect = getBoundingClientRect( el );
@@ -290,14 +325,13 @@ function offset( pos, el, target ) {
 
 /**
  * Extracted from `timoxley/offset`, but directly using a
- * TextRectangle instead of getting another version.
+ * DOMRect instead of getting another version.
  *
- * @param {TextRectangle} box - result from a `getBoundingClientRect()` call
- * @param {Document}      doc - Document instance to use
- * @return {object} an object with `top` and `left` Number properties
+ * @param {DOMRect}  box - Result from a `getBoundingClientRect()` call.
+ * @param {Document} doc - Document instance to use.
+ * @return {object} An object with `top` and `left` number properties.
  * @private
  */
-
 function _offset( box, doc ) {
 	const body = doc.body || doc.getElementsByTagName( 'body' )[ 0 ];
 	const docEl = doc.documentElement || body.parentNode;
diff --git a/projects/plugins/jetpack/_inc/client/config.js b/projects/plugins/jetpack/_inc/client/config.js
index 3de626c01622..c7c5d7d348ff 100644
--- a/projects/plugins/jetpack/_inc/client/config.js
+++ b/projects/plugins/jetpack/_inc/client/config.js
@@ -4,6 +4,14 @@ const data = {
 	google_analytics_enabled: false,
 	google_analytics_key: null,
 };
+
+/**
+ * Returns a configuration value.
+ *
+ * @param {string} key - Configuration key.
+ * @return {*} Configuration value.
+ * @throws {Error} If the key does not exist.
+ */
 function config( key ) {
 	if ( key in data ) {
 		return data[ key ];
diff --git a/projects/plugins/jetpack/_inc/client/lib/accessible-focus/index.js b/projects/plugins/jetpack/_inc/client/lib/accessible-focus/index.js
index 383c47cef608..cc451c876359 100644
--- a/projects/plugins/jetpack/_inc/client/lib/accessible-focus/index.js
+++ b/projects/plugins/jetpack/_inc/client/lib/accessible-focus/index.js
@@ -1,6 +1,9 @@
 const keyboardNavigationKeycodes = [ 9, 32, 37, 38, 39, 40 ]; // keyCodes for tab, space, left, up, right, down respectively
 let keyboardNavigation = false;
 
+/**
+ * Enables accessible focus styles when navigating via keyboard.
+ */
 function accessibleFocus() {
 	document.addEventListener( 'keydown', function ( event ) {
 		if ( keyboardNavigation ) {
diff --git a/projects/plugins/jetpack/_inc/client/mixins/emitter/index.js b/projects/plugins/jetpack/_inc/client/mixins/emitter/index.js
index c1ec66c0de04..57cfd6a808ec 100644
--- a/projects/plugins/jetpack/_inc/client/mixins/emitter/index.js
+++ b/projects/plugins/jetpack/_inc/client/mixins/emitter/index.js
@@ -1,5 +1,10 @@
 import { EventEmitter } from 'events';
 
+/**
+ * Adds EventEmitter methods to a prototype.
+ *
+ * @param {object} prototype - Prototype to extend.
+ */
 export default function ( prototype ) {
 	Object.assign( prototype, EventEmitter.prototype );
 	prototype.emitChange = function () {
diff --git a/projects/plugins/jetpack/_inc/client/my-plan/index.jsx b/projects/plugins/jetpack/_inc/client/my-plan/index.jsx
index dbbfd92d05f0..fdbb163c3208 100644
--- a/projects/plugins/jetpack/_inc/client/my-plan/index.jsx
+++ b/projects/plugins/jetpack/_inc/client/my-plan/index.jsx
@@ -15,6 +15,12 @@ import MyPlanBody from './my-plan-body';
 import MyPlanHeader from './my-plan-header';
 import MyPlanPartnerCoupon from './my-plan-partner-coupon';
 
+/**
+ * My Plan page component.
+ *
+ * @param {object} props - Component props.
+ * @return {import('react').ReactElement} React element.
+ */
 export function MyPlan( props ) {
 	let sitePlan = props.sitePlan.product_slug || '',
 		availableFeatures = props.availableFeatures,
diff --git a/projects/plugins/jetpack/_inc/twitter-timeline.js b/projects/plugins/jetpack/_inc/twitter-timeline.js
index ff3dc79f162a..d747b1265336 100644
--- a/projects/plugins/jetpack/_inc/twitter-timeline.js
+++ b/projects/plugins/jetpack/_inc/twitter-timeline.js
@@ -1,4 +1,4 @@
-! ( function ( d, s, id ) {
+void ( function ( d, s, id ) {
 	var js,
 		fjs = d.getElementsByTagName( s )[ 0 ],
 		p = /^http:/.test( d.location ) ? 'http' : 'https';
diff --git a/projects/plugins/jetpack/changelog/update-eslint-fixes b/projects/plugins/jetpack/changelog/update-eslint-fixes
new file mode 100644
index 000000000000..f8a0470dff03
--- /dev/null
+++ b/projects/plugins/jetpack/changelog/update-eslint-fixes
@@ -0,0 +1,4 @@
+Significance: patch
+Type: other
+Comment: Fix ESLint issues in legacy Jetpack admin client files.
+
diff --git a/tools/eslint-excludelist.json b/tools/eslint-excludelist.json
index 9671bc7c5724..fe51488c7066 100644
--- a/tools/eslint-excludelist.json
+++ b/tools/eslint-excludelist.json
@@ -1,11 +1 @@
-[
-	"projects/plugins/jetpack/_inc/client/components/global-notices/state/notices/actions.js",
-	"projects/plugins/jetpack/_inc/client/components/global-notices/state/notices/reducer.js",
-	"projects/plugins/jetpack/_inc/client/components/modal/index.jsx",
-	"projects/plugins/jetpack/_inc/client/components/popover/util.js",
-	"projects/plugins/jetpack/_inc/client/config.js",
-	"projects/plugins/jetpack/_inc/client/lib/accessible-focus/index.js",
-	"projects/plugins/jetpack/_inc/client/mixins/emitter/index.js",
-	"projects/plugins/jetpack/_inc/client/my-plan/index.jsx",
-	"projects/plugins/jetpack/_inc/twitter-timeline.js"
-]
+[]