diff --git a/frontend/src/components/Utils/time.js b/frontend/src/components/Utils/time.js
index fe354c26..8140ea53 100644
--- a/frontend/src/components/Utils/time.js
+++ b/frontend/src/components/Utils/time.js
@@ -1,11 +1,12 @@
 import * as firebase from 'firebase/app';
 
 /**
- * Format a timestamp (in milliseconds) into a pretty string with just the time.
+ * Format a timestamp (in milliseconds) into a pretty string with just the time like
+ * '10.19 AM'.
  *
- * @param {int} msTimestamp
- * @param {string} timezone
- * @returns {string} Time formatted into a string like '10:19 AM'.
+ * @param {int} msTimestamp Timestamp in milliseconds of desired date.
+ * @param {string} timezone Timezone in which to convert.
+ * @returns {string} Time formatted into desired pretty string.
  */
 export function timestampToTimeFormatted(msTimestamp, timezone = 'America/New_York') {
   const date = new Date(msTimestamp);
@@ -18,11 +19,12 @@ export function timestampToTimeFormatted(msTimestamp, timezone = 'America/New_Yo
 }
 
 /**
- * Format a timestamp (in milliseconds) into a pretty string with just the date.
+ * Format a timestamp (in milliseconds) into a pretty string with just the date, like
+ *  'Monday, January 19, 1970'.
  *
- * @param {int} msTimestamp
- * @param {string} timezone
- * @returns {string} Time formatted into a string like 'Monday, January 19, 1970'.
+ * @param {int} msTimestamp Timestamp in milliseconds of desired date.
+ * @param {string} timezone Timezone in which to convert.
+ * @returns {string} Time formatted into desired pretty string.
  */
 export function timestampToDateFormatted(msTimestamp, timezone='America/New_York') {
   const date = new Date(msTimestamp);
@@ -36,15 +38,15 @@ export function timestampToDateFormatted(msTimestamp, timezone='America/New_York
   return date.toLocaleDateString('en-US', formatOptions);
 }
 
-/**
- * Format a timestamp (in milliseconds) into a pretty string.
- *
- * @param {int} msTimestamp
- * @param {string} timezone
- * @returns {string} Time formatted into a string like
- * "Monday, January 19, 1970, 02:48 AM"
+/** 
+ * Format a timestamp (in milliseconds) into a pretty string like 
+ * 'Monday, January 19, 1970, 02:48 AM'.
+ * 
+ * @param {int} msTimestamp Timestamp in milliseconds of desired date.
+ * @param {string} timezone Timezone in which to convert.
+ * @returns {string} Time formatted into desired pretty string.
  */
-export function timestampToFormatted(msTimestamp, timezone = "America/New_York") {
+export function timestampToFormatted(msTimestamp, timezone = 'America/New_York') {
   let date = new Date(msTimestamp);
   let formatOptions = {
     weekday: 'long',
diff --git a/frontend/src/components/Utils/time.test.js b/frontend/src/components/Utils/time.test.js
index 73098453..b02a9102 100644
--- a/frontend/src/components/Utils/time.test.js
+++ b/frontend/src/components/Utils/time.test.js
@@ -45,15 +45,15 @@ test('other time timestamp format', () => {
 test('new york full timestamp format', () => {
   // Month parameter is zero indexed so it's actually the 10th month.
   const testDate = new Date(Date.UTC(2020, 9, 3, 14, 19, 4, 23)).getTime();
-  const expected = "Saturday, October 3, 2020, 10:19 AM";
+  const expected = 'Saturday, October 3, 2020, 10:19 AM';
   const actual = utils.timestampToFormatted(testDate);
   expect(actual).toEqual(expected);
 });
 
 test('other full timestamp format', () => {
   const testDate = new Date(Date.UTC(2020, 7, 23, 2, 3, 2, 4)).getTime();
-  const expectedCentral = "Saturday, August 22, 2020, 9:03 PM";
-  const expectedSingapore = "Sunday, August 23, 2020, 10:03 AM";
+  const expectedCentral = 'Saturday, August 22, 2020, 9:03 PM';
+  const expectedSingapore = 'Sunday, August 23, 2020, 10:03 AM';
   const actualCentral = utils.timestampToFormatted(testDate, TZ_CHICAGO);
   const actualSingapore = utils.timestampToFormatted(testDate, TZ_SINGAPORE);
   expect(actualCentral).toEqual(expectedCentral);
diff --git a/frontend/src/components/ViewActivities/activity.js b/frontend/src/components/ViewActivities/activity.js
index 0aee66e3..862102ec 100644
--- a/frontend/src/components/ViewActivities/activity.js
+++ b/frontend/src/components/ViewActivities/activity.js
@@ -2,11 +2,13 @@ import React from 'react';
 import * as time from '../Utils/time.js';
 import * as DB from '../../constants/database.js'
 import '../../styles/activities.css';
-import { getField } from './activityfns.js';
+import { getField, writeActivity } from './activityfns.js';
 import { Accordion, Button, Card, Col, Form, Row } from 'react-bootstrap';
 
 /**
- * Returns a dropdown of all the timezones.
+ * Return a dropdown of all the timezones.
+ * 
+ * @return {HTML} Dropdown of all the timezones.
  */
 function timezonePicker() {
   // TODO: Make this dropdown. (#51)
@@ -14,13 +16,14 @@ function timezonePicker() {
 }
 
 /**
- * A single activity. 
+ * React component for a single activity. 
  * 
- * @param {Object} props This component expects the following props:
- * - `activity` The activity to display.
+ * @property {Object} props ReactJS props. 
+ * @property {ActivityInfo} props.activity The activity to display.
+ *    (MUST contain 'id' field with database activity id and 'tripId' field.)
  */
 class Activity extends React.Component {
-  /** {@inheritdoc} */
+  /** @override */
   constructor(props) {
     super(props);
 
@@ -30,6 +33,32 @@ class Activity extends React.Component {
     this.setEditActivity = this.setEditActivity.bind(this);
     this.finishEditActivity = this.finishEditActivity.bind(this);
     this.displayCard = this.displayCard.bind(this);
+    this.editActivity = this.editActivity.bind(this);
+
+    // References. 
+    this.editTitleRef = React.createRef();
+    this.editStartDateRef = React.createRef();
+    this.editEndDateRef = React.createRef();
+    this.editStartTimeRef = React.createRef();
+    this.editEndTimeRef = React.createRef();
+    this.editDescriptionRef = React.createRef();
+  }
+
+  /**
+   * Edit an activity in the database upon form submission.
+   * TODO: Update times as well! This only does the text field forms (#64).
+   */
+  editActivity() {
+    let newVals = {};
+    if (this.editTitleRef.current.value !== '') {
+      newVals[DB.ACTIVITIES_TITLE] = this.editTitleRef.current.value;
+    }
+    if (this.editDescriptionRef.current.value !== '') {
+      newVals[DB.ACTIVITIES_DESCRIPTION] = this.editDescriptionRef.current.value;
+    }
+    if (Object.keys(newVals).length !== 0) {
+      writeActivity(this.props.activity.tripId, this.props.activity.id, newVals);
+    }
   }
 
   /**
@@ -41,10 +70,14 @@ class Activity extends React.Component {
 
   /**
    * Set the activity into viewing mode.
+   * 
+   * @param {event} event The form's event.
    */
-  finishEditActivity() { 
+  finishEditActivity(event) {
     this.setState({editing: false});
-  }
+    event.preventDefault();
+    this.editActivity();
+  };
 
   /**
    * Display the current activity, either in view or display mode.
@@ -61,42 +94,43 @@ class Activity extends React.Component {
     } else { // Edit mode.
       return (
         // TODO: Save form. (#48)
-        <Form className="activity-editor" onSubmit={this.finishEditActivity}>
-          <Form.Group as={Row} controlId="formActivityTitle">
+        <Form className='activity-editor' onSubmit={this.finishEditActivity}>
+          <Form.Group as={Row} controlId='formActivityTitle'>
             <Col sm={2}><Form.Label>Title:</Form.Label></Col>
-            <Col><Form.Control type="text" placeholder={activity[DB.ACTIVITIES_TITLE]}/></Col>
+            <Col><Form.Control type='text' placeholder={activity[DB.ACTIVITIES_TITLE]} ref={this.editTitleRef}/></Col>
           </Form.Group>
-          <Form.Group as={Row} controlId="formActivityStartTime">
+          <Form.Group as={Row} controlId='formActivityStartTime'>
             <Col sm={2}><Form.Label>From:</Form.Label></Col>
-            <Col sm={4}><Form.Control type="date" label="date"/></Col>
-            <Col sm={2}><Form.Control type="time" label="time"/></Col>
+            <Col sm={4}><Form.Control type='date' label='date' ref={this.editStartDateRef}/></Col>
+            <Col sm={2}><Form.Control type='time' label='time' ref={this.editStartTimeRef}/></Col>
             <Col sm={1}>{timezonePicker()}</Col>
           </Form.Group>
-          <Form.Group as={Row} controlId="formActivityEndTime">
+          <Form.Group as={Row} controlId='formActivityEndTime'>
             <Col sm={2}><Form.Label>To:</Form.Label></Col>
-            <Col sm={4}><Form.Control type="date" label="date"/></Col>
-            <Col sm={2}><Form.Control type="time" label="time"/></Col>
+            <Col sm={4}><Form.Control type='date' label='date' ref={this.editEndDateRef}/></Col>
+            <Col sm={2}><Form.Control type='time' label='time' ref={this.editEndTimeRef}/></Col>
             <Col sm={1}>{timezonePicker()}</Col>
           </Form.Group>
-          <Form.Group as={Row} controlId="formActivityDescription">
+          <Form.Group as={Row} controlId='formActivityDescription'>
             <Col sm={2}><Form.Label>Description:</Form.Label></Col>
-            <Col><Form.Control type="text" 
-              placeholder={getField(activity, DB.ACTIVITIES_DESCRIPTION, "Add some details!") }/>
+            <Col><Form.Control type='text' 
+              placeholder={getField(activity, DB.ACTIVITIES_DESCRIPTION, 'Add some details!')}
+              ref={this.editDescriptionRef} />
             </Col>
           </Form.Group>
-          <Button type="submit" className="float-right">Done!</Button>
+          <Button type='submit' className='float-right'>Done!</Button>
         </Form>
       )
     }
   }
 
-  /** @inheritdoc */
+  /** @override */
   render() {
     const activity = this.props.activity;
     return (
       <Accordion defaultActiveKey='1'>  
         <Card>
-          <Accordion.Toggle as={Card.Header} eventKey='0' align='center' >
+          <Accordion.Toggle as={Card.Header} eventKey='0' align='center'>
             {activity[DB.ACTIVITIES_TITLE]}
           </Accordion.Toggle>
           <Accordion.Collapse eventKey='0' className={'view-activity' + (this.state.editing? ' edit': '')}>
diff --git a/frontend/src/components/ViewActivities/activityday.js b/frontend/src/components/ViewActivities/activityday.js
index e4ca85cb..58b221ca 100644
--- a/frontend/src/components/ViewActivities/activityday.js
+++ b/frontend/src/components/ViewActivities/activityday.js
@@ -4,24 +4,23 @@ import * as activityFns from './activityfns.js';
 import * as time from '../Utils/time.js'
 
 /**
- * One single day of activities.
- *
- * @param {Object} props This component expects the following props:
- * - `activities` The list of activities for "today".
- * - `date` The date, formatted as "MM/DD/YYYY".
+ * React component for a single day of activities. 
+ * 
+ * @property {Object} props ReactJS props. 
+ * @property {ActivityInfo[]} props.activities The list of activities for 'today'.
+ * @property {string} props.date The date, formatted as 'MM/DD/YYYY'.
  */
 class ActivityDay extends React.Component {
-  /** @inheritdoc */
+  /** @override */
   render() {
     const sortedActivities = Array.from(this.props.activities)
           .sort(activityFns.compareActivities);
     let date = new Date(this.props.date);
-    // let id = date.getTime();
     return (
       <div className='activity-day'>
         <h4>{time.timestampToDateFormatted(date.getTime())}</h4>
         {sortedActivities.map((activity, index) => (
-          <Activity activity={activity} key={index} className="activity"/>
+          <Activity activity={activity} key={index} className='activity'/>
         ))}
       </div>
     );
diff --git a/frontend/src/components/ViewActivities/activityfns.js b/frontend/src/components/ViewActivities/activityfns.js
index ba75365e..c77c6282 100644
--- a/frontend/src/components/ViewActivities/activityfns.js
+++ b/frontend/src/components/ViewActivities/activityfns.js
@@ -1,12 +1,39 @@
 import * as DB from '../../constants/database.js';
+import app from '../Firebase';
+import { firestore } from 'firebase';
+
+const db = app.firestore();
+
+/**
+ * An activity object. 
+ * @typedef {Object} ActivityInfo
+ * @property {string} id The activity's ID in the database.
+ * @property {string} tripId The activity's tripId in the database.
+ * @property {string} title The activity's title.
+ * @property {long} start_time Number of seconds since epoch of activity's start time.
+ * @property {long} end_time Number of seconds since epoch of activity's end time.
+ * @property {string} [description] The activity's description.
+ */
+
+/**
+ * A single activity day. A single instance looks like:
+ * <pre><code> ['MM/DD/YYYY', [activities on that day]] </code></pre>
+ * @typedef {Array.<string, ActivityInfo[]>} DayOfActivities
+ * 
+ */
 
 /**
  * Sort a list of trip activities by date. 
- * @param {Array} tripActivities Array of activities.
- * @returns List of trip activities in the form
- * [ ['MM/DD/YYYY', [activities on that day]], ...] in chronological order by date.
+ * @param {ActivityInfo[]} tripActivities Array of activities.
+ * @return {DayOfActivities[]} List of trip activities in the form
+ * <pre><code>[ , ...]</code></pre>
+ * in chronological order by date.
  */
 export function sortByDate(tripActivities) {
+  if (tripActivities === undefined) {
+    return null;
+  }
+  console.log(tripActivities);
   let activities = new Map(); // { MM/DD/YYYY: [activities] }.
   for (let activity of tripActivities) {
     const activityDate = new Date(activity[DB.ACTIVITIES_START_TIME]);
@@ -19,15 +46,18 @@ export function sortByDate(tripActivities) {
   }
 
   // Sort activities by date.
+  console.log(activities);
   let activitiesSorted = Array.from(activities).sort(compareActivities);
   
   return activitiesSorted;
 }
 
 /**
- * Put a and b in display order. 
- * @param {dictionary} a Dictionary representing activity a and its fields. 
- * @param {dictionary} b Dictionary representing activity b and its fields.
+ * Put <code>a</code> and <code>b</code> in display order. 
+ * This function is a comparator.
+ * @param {ActivityInfo} a Dictionary representing activity a and its fields. 
+ * @param {ActivityInfo} b Dictionary representing activity b and its fields.
+ * @return {int} <code>-1</code> if <code>a</code> comes before <code>b</code>, else <code>1</code>. 
  */
 export function compareActivities(a, b) {
   if (a[DB.ACTIVITIES_START_TIME] < b[DB.ACTIVITIES_START_TIME]) {
@@ -44,14 +74,42 @@ export function compareActivities(a, b) {
 /**
  * Get the field of field name `fieldName` from `activity` or the default value.
  * 
- * @param {Object} activity 
- * @param {string} fieldName 
- * @param defaultValue 
- * @returns `activity[fieldName]` if possible, else `defaultValue`.
+ * @param {ActivityInfo} activity The activity from which to get the field.
+ * @param {string} fieldName Name of field to get.
+ * @param {*} defaultValue Value if field is not found/is null.
+ * @return {*} <code>activity[fieldName]</code> if possible, else <code>defaultValue</code>.
  */
 export function getField(activity, fieldName, defaultValue) {
   if (activity[fieldName] === null || activity[fieldName] === undefined) {
     return defaultValue;
   }
   return activity[fieldName];
+}
+
+/**
+ * Write contents into an activity already existing in the database.
+ * 
+ * @param {string} tripId Database ID of the trip whose actiivty should be modified.
+ * @param {string} activityId Database ID of the activity to be modified.
+ * @param {Object} newValues Dictionary of the new values in <code>{fieldName: newValue}</code> form
+ * @return {boolean} <code>true</code> if the write was successful, <code>false</code> otherwise. 
+ */
+export async function writeActivity(tripId, activityId, newValues) {
+  // todo: check if tripId or activityId is not valid. (#58)
+  newValues = {
+    ...newValues, 
+    'fillerstamp': firestore.Timestamp.now()
+  };
+
+  const act = db.collection(DB.COLLECTION_TRIPS).doc(tripId)
+    .collection(DB.COLLECTION_ACTIVITIES).doc(activityId);
+  
+  try {
+    // Note: newValues cannot contain lists. Check documentation for update().
+    await act.update(newValues);
+    return true;
+  } catch (e) {
+    console.log(e);
+    return false;
+  }
 }
\ No newline at end of file
diff --git a/frontend/src/components/ViewActivities/activityfns.test.js b/frontend/src/components/ViewActivities/activityfns.test.js
index 8cd69333..99d82ade 100644
--- a/frontend/src/components/ViewActivities/activityfns.test.js
+++ b/frontend/src/components/ViewActivities/activityfns.test.js
@@ -93,7 +93,7 @@ describe('sortByDate tests', () => {
 })
 
 test('getField', () => {
-  const activity = {field1: "yes"};
-  expect(activityFns.getField(activity, "field1", "nooo")).toBe("yes");
-  expect(activityFns.getField(activity, "field2", 4)).toBe(4);
+  const activity = {field1: 'yes'};
+  expect(activityFns.getField(activity, 'field1', 'nooo')).toBe('yes');
+  expect(activityFns.getField(activity, 'field2', 4)).toBe(4);
 })
\ No newline at end of file
diff --git a/frontend/src/components/ViewActivities/activitylist.js b/frontend/src/components/ViewActivities/activitylist.js
index fd34e098..068c0312 100644
--- a/frontend/src/components/ViewActivities/activitylist.js
+++ b/frontend/src/components/ViewActivities/activitylist.js
@@ -7,23 +7,25 @@ import app from '../Firebase';
 
 const db = app.firestore();
 
-
 /**
  * Gets the list of activities from the server. 
  * 
  * @param {string} tripId The trip ID.
+ * @return {ActivityInfo[]} The list of trip activities.
  */
 export async function getActivityList(tripId) {
-  let tripActivities = [];
-  
-  return db.collection(DB.COLLECTION_TRIPS).doc(tripId)
-  .collection(DB.COLLECTION_ACTIVITIES).get()
-  .then(querySnapshot => {
-    querySnapshot.forEach(doc => {
-      let data = doc.data();
-      data['id'] = doc.id;
-      
-      // TODO: if start date != end date, split into 2 days. (#37)
+    let tripActivities = [];
+    
+    return db.collection(DB.COLLECTION_TRIPS).doc(tripId)
+    .collection(DB.COLLECTION_ACTIVITIES).get()
+    .then(querySnapshot => {
+      querySnapshot.forEach(doc => {
+        console.log(doc.data());
+        let data = doc.data();
+        data['id'] = doc.id;
+        data['tripId'] = tripId;
+        
+        // TODO: if start date != end date, split into 2 days. (#37)
 
       // Eliminate nanoseconds, convert to milliseconds.
       data[DB.ACTIVITIES_START_TIME] =
@@ -32,28 +34,26 @@ export async function getActivityList(tripId) {
         data[DB.ACTIVITIES_END_TIME]['seconds'] * 1000;
 
       tripActivities.push(data);
-    })
-  }).catch(error => {
-    console.log("It seems that an error has occured.");
-    tripActivities = null;
-  }).then( () => {return tripActivities} );
+    });
+    return tripActivities;
+  });
 }
 
 /**
- * The list of activities. 
+ * React component for the list of activities. 
  * 
- * @param {Object} props This component expects the following props:
- * - `tripId` {string} The trip's ID.  
+ * @param {Object} props ReactJS props. 
+ * @param {string} props.tripId The trip's ID.  
  */
 class ActivityList extends React.Component {
-  /** @inheritdoc */
+  /** @override */
   constructor(props) {
     super(props);
     this.state = { days : [] };
   }
 
   /** 
-   * @inheritdoc
+   * @override
    * 
    * Get sorted list of activities from the database. 
    * 
@@ -71,9 +71,10 @@ class ActivityList extends React.Component {
       return;
     } 
     this.setState({days: activityFns.sortByDate(tripActivities)});
+    console.log(this.state.days);
   }
 
-  /** @inheritdoc */
+  /** @override */
   render() {
     if (this.state === null) { return (<div></div>); }
     if (this.state.days === null) {