Want to do "autocomplete" for cities in a webform? Using the <datalist> tag, you can use this ...

index.html

<input list="cities" name="city" size="25" placeholder="city">

<datalist id="cities">
  <option value="Aberdeen">
  <option value="Abilene">
  <option value="Aguada">
  <option value="Aguas">
  <option value="Aibonito">
  <option value="Akron">
  <option value="Albany">
  <option value="Albuquerque">
  <option value="Alexandria">
  <option value="Allentown">
  <option value="Alta">
  <option value="Alto">
  <option value="Amarillo">
  <option value="Anaheim">
  <option value="Anchorage">
  <option value="Ann Arbor">
  <option value="Antioch">
  <option value="Apple Valley">
  <option value="Appleton">
  <option value="Arlington">
  <option value="Arroyo">
  <option value="Arvada">
  <option value="Asheville">
  <option value="Athens">
  <option value="Atlanta">
  <option value="Atlantic City">
  <option value="Augusta">
  <option value="Aurora">
  <option value="Austin">
  <option value="Baja">
  <option value="Bakersfield">
  <option value="Baltimore">
  <option value="Barceloneta">
  <option value="Barnstable">
  <option value="Baton Rouge">
  <option value="Bayamón">
  <option value="Beaumont">
  <option value="Bel Air">
  <option value="Bellevue">
  <option value="Berkeley">
  <option value="Bethlehem">
  <option value="Billings">
  <option value="Birmingham">
  <option value="Bloomington">
  <option value="Boise">
  <option value="Boise City">
  <option value="Bonita Springs">
  <option value="Boston">
  <option value="Boulder">
  <option value="Bradenton">
  <option value="Bremerton">
  <option value="Bridgeport">
  <option value="Brighton">
  <option value="Brownsville">
  <option value="Bryan">
  <option value="Buffalo">
  <option value="Burbank">
  <option value="Burlington">
  <option value="Cambridge">
  <option value="Camuy">
  <option value="Canton">
  <option value="Cape Coral">
  <option value="Carolina">
  <option value="Carrollton">
  <option value="Cary">
  <option value="Cathedral City">
  <option value="Cayey">
  <option value="Cedar Rapids">
  <option value="Champaign">
  <option value="Chandler">
  <option value="Charleston">
  <option value="Charlotte">
  <option value="Chattanooga">
  <option value="Chesapeake">
  <option value="Chicago">
  <option value="Chula Vista">
  <option value="Ciales">
  <option value="Cincinnati">
  <option value="Clarke County">
  <option value="Clarksville">
  <option value="Clearwater">
  <option value="Cleveland">
  <option value="Coamo">
  <option value="College Station">
  <option value="Colorado Springs">
  <option value="Columbia">
  <option value="Columbus">
  <option value="Concord">
  <option value="Coral Springs">
  <option value="Corona">
  <option value="Corozal">
  <option value="Corpus Christi">
  <option value="Costa Mesa">
  <option value="Dallas">
  <option value="Daly City">
  <option value="Danbury">
  <option value="Davenport">
  <option value="Davidson County">
  <option value="Dayton">
  <option value="Daytona Beach">
  <option value="Deltona">
  <option value="Denton">
  <option value="Denver">
  <option value="Des Moines">
  <option value="Detroit">
  <option value="Dorado">
  <option value="Downey">
  <option value="Duluth">
  <option value="Durham">
  <option value="Díaz">
  <option value="El Monte">
  <option value="El Paso">
  <option value="Elizabeth">
  <option value="Elk Grove">
  <option value="Elkhart">
  <option value="Erie">
  <option value="Escondido">
  <option value="Eugene">
  <option value="Evansville">
  <option value="Fairfield">
  <option value="Fargo">
  <option value="Fayetteville">
  <option value="Fitchburg">
  <option value="Flint">
  <option value="Florida">
  <option value="Fontana">
  <option value="Fort Collins">
  <option value="Fort Lauderdale">
  <option value="Fort Smith">
  <option value="Fort Walton Beach">
  <option value="Fort Wayne">
  <option value="Fort Worth">
  <option value="Frederick">
  <option value="Fremont">
  <option value="Fresno">
  <option value="Fullerton">
  <option value="Gainesville">
  <option value="Garden Grove">
  <option value="Garland">
  <option value="Gastonia">
  <option value="Germán">
  <option value="Gilbert">
  <option value="Glendale">
  <option value="Grand Prairie">
  <option value="Grand Rapids">
  <option value="Grayslake">
  <option value="Green Bay">
  <option value="GreenBay">
  <option value="Greensboro">
  <option value="Greenville">
  <option value="Guayanilla">
  <option value="Gulfport-Biloxi">
  <option value="Gurabo">
  <option value="Hagerstown">
  <option value="Hampton">
  <option value="Harlingen">
  <option value="Harrisburg">
  <option value="Hartford">
  <option value="Hatillo">
  <option value="Havre de Grace">
  <option value="Hayward">
  <option value="Hemet">
  <option value="Henderson">
  <option value="Hesperia">
  <option value="Hialeah">
  <option value="Hickory">
  <option value="High Point">
  <option value="Hollywood">
  <option value="Honolulu">
  <option value="Houma">
  <option value="Houston">
  <option value="Howell">
  <option value="Humacao">
  <option value="Huntington">
  <option value="Huntington Beach">
  <option value="Huntsville">
  <option value="Independence">
  <option value="Indianapolis">
  <option value="Inglewood">
  <option value="Irvine">
  <option value="Irving">
  <option value="Isabel">
  <option value="Jackson">
  <option value="Jacksonville">
  <option value="Jayuya">
  <option value="Jefferson">
  <option value="Jersey City">
  <option value="Johnson City">
  <option value="Joliet">
  <option value="Juan">
  <option value="Kailua">
  <option value="Kalamazoo">
  <option value="Kaneohe">
  <option value="Kansas City">
  <option value="Kennewick">
  <option value="Kenosha">
  <option value="Killeen">
  <option value="Kissimmee">
  <option value="Knoxville">
  <option value="Lacey">
  <option value="Lafayette">
  <option value="Lajas">
  <option value="Lake Charles">
  <option value="Lakeland">
  <option value="Lakewood">
  <option value="Lancaster">
  <option value="Lansing">
  <option value="Laredo">
  <option value="Las">
  <option value="Las">
  <option value="Las Cruces">
  <option value="Las Vegas">
  <option value="Layton">
  <option value="Leominster">
  <option value="Lewisville">
  <option value="Lexington">
  <option value="Lincoln">
  <option value="Little Rock">
  <option value="Loiza">
  <option value="Long Beach">
  <option value="Lorain">
  <option value="Lorenzo">
  <option value="Los Angeles">
  <option value="Louisville">
  <option value="Lowell">
  <option value="Lubbock">
  <option value="Macon">
  <option value="Madison">
  <option value="Manatí">
  <option value="Manchester">
  <option value="Marina">
  <option value="Marysville">
  <option value="Maunabo">
  <option value="McAllen">
  <option value="McHenry">
  <option value="Medford">
  <option value="Melbourne">
  <option value="Memphis">
  <option value="Merced">
  <option value="Mesa">
  <option value="Mesquite">
  <option value="Miami">
  <option value="Milwaukee">
  <option value="Minneapolis">
  <option value="Miramar">
  <option value="Mission Viejo">
  <option value="Mobile">
  <option value="Moca">
  <option value="Modesto">
  <option value="Monroe">
  <option value="Monterey">
  <option value="Montgomery">
  <option value="Moreno Valley">
  <option value="Murfreesboro">
  <option value="Murrieta">
  <option value="Muskegon">
  <option value="Myrtle Beach">
  <option value="Naguabo">
  <option value="Naperville">
  <option value="Naples">
  <option value="Nashua">
  <option value="Nashville">
  <option value="New Bedford">
  <option value="New Haven">
  <option value="New London">
  <option value="New Orleans">
  <option value="New York">
  <option value="New York City">
  <option value="Newark">
  <option value="Newburgh">
  <option value="Newport News">
  <option value="Norfolk">
  <option value="Normal">
  <option value="Norman">
  <option value="North Charleston">
  <option value="North Las Vegas">
  <option value="North Port">
  <option value="Norwalk">
  <option value="Norwich">
  <option value="Oakland">
  <option value="Ocala">
  <option value="Oceanside">
  <option value="Odessa">
  <option value="Ogden">
  <option value="Oklahoma City">
  <option value="Olathe">
  <option value="Olympia">
  <option value="Omaha">
  <option value="Ontario">
  <option value="Orange">
  <option value="Orem">
  <option value="Orlando">
  <option value="Orocovis">
  <option value="Overland Park">
  <option value="Oxnard">
  <option value="Palm Bay">
  <option value="Palm Springs">
  <option value="Palmdale">
  <option value="Panama City">
  <option value="Pasadena">
  <option value="Paterson">
  <option value="Pembroke Pines">
  <option value="Pensacola">
  <option value="Peoria">
  <option value="Peñuelas">
  <option value="Philadelphia">
  <option value="Phoenix">
  <option value="Pittsburgh">
  <option value="Plano">
  <option value="Pomona">
  <option value="Pompano Beach">
  <option value="Port Arthur">
  <option value="Port Orange">
  <option value="Port Saint Lucie">
  <option value="Port St. Lucie">
  <option value="Portland">
  <option value="Portsmouth">
  <option value="Poughkeepsie">
  <option value="Providence">
  <option value="Provo">
  <option value="Pueblo">
  <option value="Punta Gorda">
  <option value="Quebradillas">
  <option value="Racine">
  <option value="Raleigh">
  <option value="Rancho Cucamonga">
  <option value="Reading">
  <option value="Redding">
  <option value="Reno">
  <option value="Richland">
  <option value="Richmond">
  <option value="Richmond County">
  <option value="Rio">
  <option value="Riverside">
  <option value="Roanoke">
  <option value="Rochester">
  <option value="Rockford">
  <option value="Rojo">
  <option value="Roseville">
  <option value="Round Lake Beach">
  <option value="Sabana">
  <option value="Sacramento">
  <option value="Saginaw">
  <option value="Saint Louis">
  <option value="Saint Paul">
  <option value="Saint Petersburg">
  <option value="Salem">
  <option value="Salinas">
  <option value="Salinas">
  <option value="Salt Lake City">
  <option value="San Antonio">
  <option value="San Bernardino">
  <option value="San Buenaventura">
  <option value="San Diego">
  <option value="San Francisco">
  <option value="San Jose">
  <option value="Santa Ana">
  <option value="Santa Barbara">
  <option value="Santa Clara">
  <option value="Santa Clarita">
  <option value="Santa Cruz">
  <option value="Santa Maria">
  <option value="Santa Rosa">
  <option value="Sarasota">
  <option value="Savannah">
  <option value="Scottsdale">
  <option value="Scranton">
  <option value="Seaside">
  <option value="Seattle">
  <option value="Sebastian">
  <option value="Sebastián">
  <option value="Shreveport">
  <option value="Simi Valley">
  <option value="Sioux City">
  <option value="Sioux Falls">
  <option value="South Bend">
  <option value="South Lyon">
  <option value="Spartanburg">
  <option value="Spokane">
  <option value="Springdale">
  <option value="Springfield">
  <option value="St. Louis">
  <option value="St. Paul">
  <option value="St. Petersburg">
  <option value="Stamford">
  <option value="Sterling Heights">
  <option value="Stockton">
  <option value="Sunnyvale">
  <option value="Syracuse">
  <option value="Tacoma">
  <option value="Tallahassee">
  <option value="Tampa">
  <option value="Temecula">
  <option value="Tempe">
  <option value="Thornton">
  <option value="Thousand Oaks">
  <option value="Toledo">
  <option value="Topeka">
  <option value="Torrance">
  <option value="Trenton">
  <option value="Tucson">
  <option value="Tulsa">
  <option value="Tuscaloosa">
  <option value="Tyler">
  <option value="Utica">
  <option value="Vallejo">
  <option value="Vancouver">
  <option value="Vega">
  <option value="Vega">
  <option value="Vero Beach">
  <option value="Victorville">
  <option value="Vieques">
  <option value="Virginia Beach">
  <option value="Visalia">
  <option value="Waco">
  <option value="Warren">
  <option value="Washington">
  <option value="Waterbury">
  <option value="Waterloo">
  <option value="West Covina">
  <option value="West Valley City">
  <option value="Westminster">
  <option value="Wichita">
  <option value="Wilmington">
  <option value="Winston">
  <option value="Winter Haven">
  <option value="Worcester">
  <option value="Yabucoa">
  <option value="Yakima">
  <option value="Yauco">
  <option value="Yonkers">
  <option value="York">
  <option value="Youngstown">
</datalist>