country select javascript check which option is selected

HTML

<select name="countries" id="country_select"><option name="AF">Afghanistan</option><option name="AX">Aland Islands</option><option name="AL">Albania</option><option name="DZ">Algeria</option><option name="AS">American Samoa</option><option name="AD">Andorra</option><option name="AO">Angola</option><option name="AI">Anguilla</option><option name="AQ">Antarctica</option><option name="AG">Antigua And Barbuda</option><option name="AR">Argentina</option><option name="AM">Armenia</option><option name="AW">Aruba</option><option name="AU">Australia</option><option name="AT">Austria</option><option name="AZ">Azerbaijan</option><option name="BS">Bahamas</option><option name="BH">Bahrain</option><option name="BD">Bangladesh</option><option name="BB">Barbados</option><option name="BY">Belarus</option><option name="BE">Belgium</option><option name="BZ">Belize</option><option name="BJ">Benin</option><option name="BM">Bermuda</option><option name="BT">Bhutan</option><option name="BO">Bolivia</option><option name="BA">Bosnia And Herzegovina</option><option name="BW">Botswana</option><option name="BV">Bouvet Island</option><option name="BR">Brazil</option><option name="IO">British Indian Ocean Territory</option><option name="BN">Brunei Darussalam</option><option name="BG">Bulgaria</option><option name="BF">Burkina Faso</option><option name="BI">Burundi</option><option name="KH">Cambodia</option><option name="CM">Cameroon</option><option name="CA">Canada</option><option name="CV">Cape Verde</option><option name="KY">Cayman Islands</option><option name="CF">Central African Republic</option><option name="TD">Chad</option><option name="CL">Chile</option><option name="CN">China</option><option name="CX">Christmas Island</option><option name="CC">Cocos (Keeling) Islands</option><option name="CO">Colombia</option><option name="KM">Comoros</option><option name="CG">Congo</option><option name="CD">Congo, Democratic Republic</option><option name="CK">Cook Islands</option><option name="CR">Costa Rica</option><option name="CI">Cote D'Ivoire</option><option name="HR">Croatia</option><option name="CU">Cuba</option><option name="CY">Cyprus</option><option name="CZ">Czech Republic</option><option name="DK">Denmark</option><option name="DJ">Djibouti</option><option name="DM">Dominica</option><option name="DO">Dominican Republic</option><option name="EC">Ecuador</option><option name="EG">Egypt</option><option name="SV">El Salvador</option><option name="GQ">Equatorial Guinea</option><option name="ER">Eritrea</option><option name="EE">Estonia</option><option name="ET">Ethiopia</option><option name="FK">Falkland Islands (Malvinas)</option><option name="FO">Faroe Islands</option><option name="FJ">Fiji</option><option name="FI">Finland</option><option name="FR">France</option><option name="GF">French Guiana</option><option name="PF">French Polynesia</option><option name="TF">French Southern Territories</option><option name="GA">Gabon</option><option name="GM">Gambia</option><option name="GE">Georgia</option><option name="DE">Germany</option><option name="GH">Ghana</option><option name="GI">Gibraltar</option><option name="GR">Greece</option><option name="GL">Greenland</option><option name="GD">Grenada</option><option name="GP">Guadeloupe</option><option name="GU">Guam</option><option name="GT">Guatemala</option><option name="GG">Guernsey</option><option name="GN">Guinea</option><option name="GW">Guinea-Bissau</option><option name="GY">Guyana</option><option name="HT">Haiti</option><option name="HM">Heard Island &amp; Mcdonald Islands</option><option name="VA">Holy See (Vatican City State)</option><option name="HN">Honduras</option><option name="HK">Hong Kong</option><option name="HU">Hungary</option><option name="IS">Iceland</option><option name="IN">India</option><option name="ID">Indonesia</option><option name="IR">Iran, Islamic Republic Of</option><option name="IQ">Iraq</option><option name="IE">Ireland</option><option name="IM">Isle Of Man</option><option name="IL">Israel</option><option name="IT">Italy</option><option name="JM">Jamaica</option><option name="JP">Japan</option><option name="JE">Jersey</option><option name="JO">Jordan</option><option name="KZ">Kazakhstan</option><option name="KE">Kenya</option><option name="KI">Kiribati</option><option name="KR">Korea</option><option name="KW">Kuwait</option><option name="KG">Kyrgyzstan</option><option name="LA">Lao People's Democratic Republic</option><option name="LV">Latvia</option><option name="LB">Lebanon</option><option name="LS">Lesotho</option><option name="LR">Liberia</option><option name="LY">Libyan Arab Jamahiriya</option><option name="LI">Liechtenstein</option><option name="LT">Lithuania</option><option name="LU">Luxembourg</option><option name="MO">Macao</option><option name="MK">Macedonia</option><option name="MG">Madagascar</option><option name="MW">Malawi</option><option name="MY">Malaysia</option><option name="MV">Maldives</option><option name="ML">Mali</option><option name="MT">Malta</option><option name="MH">Marshall Islands</option><option name="MQ">Martinique</option><option name="MR">Mauritania</option><option name="MU">Mauritius</option><option name="YT">Mayotte</option><option name="MX">Mexico</option><option name="FM">Micronesia, Federated States Of</option><option name="MD">Moldova</option><option name="MC">Monaco</option><option name="MN">Mongolia</option><option name="ME">Montenegro</option><option name="MS">Montserrat</option><option name="MA">Morocco</option><option name="MZ">Mozambique</option><option name="MM">Myanmar</option><option name="NA">Namibia</option><option name="NR">Nauru</option><option name="NP">Nepal</option><option name="NL">Netherlands</option><option name="AN">Netherlands Antilles</option><option name="NC">New Caledonia</option><option name="NZ">New Zealand</option><option name="NI">Nicaragua</option><option name="NE">Niger</option><option name="NG">Nigeria</option><option name="NU">Niue</option><option name="NF">Norfolk Island</option><option name="MP">Northern Mariana Islands</option><option name="NO">Norway</option><option name="OM">Oman</option><option name="PK">Pakistan</option><option name="PW">Palau</option><option name="PS">Palestinian Territory, Occupied</option><option name="PA">Panama</option><option name="PG">Papua New Guinea</option><option name="PY">Paraguay</option><option name="PE">Peru</option><option name="PH">Philippines</option><option name="PN">Pitcairn</option><option name="PL">Poland</option><option name="PT">Portugal</option><option name="PR">Puerto Rico</option><option name="QA">Qatar</option><option name="RE">Reunion</option><option name="RO">Romania</option><option name="RU">Russian Federation</option><option name="RW">Rwanda</option><option name="BL">Saint Barthelemy</option><option name="SH">Saint Helena</option><option name="KN">Saint Kitts And Nevis</option><option name="LC">Saint Lucia</option><option name="MF">Saint Martin</option><option name="PM">Saint Pierre And Miquelon</option><option name="VC">Saint Vincent And Grenadines</option><option name="WS">Samoa</option><option name="SM">San Marino</option><option name="ST">Sao Tome And Principe</option><option name="SA">Saudi Arabia</option><option name="SN">Senegal</option><option name="RS">Serbia</option><option name="SC">Seychelles</option><option name="SL">Sierra Leone</option><option name="SG">Singapore</option><option name="SK">Slovakia</option><option name="SI">Slovenia</option><option name="SB">Solomon Islands</option><option name="SO">Somalia</option><option name="ZA">South Africa</option><option name="GS">South Georgia And Sandwich Isl.</option><option name="ES">Spain</option><option name="LK">Sri Lanka</option><option name="SD">Sudan</option><option name="SR">Suriname</option><option name="SJ">Svalbard And Jan Mayen</option><option name="SZ">Swaziland</option><option name="SE">Sweden</option><option name="CH">Switzerland</option><option name="SY">Syrian Arab Republic</option><option name="TW">Taiwan</option><option name="TJ">Tajikistan</option><option name="TZ">Tanzania</option><option name="TH">Thailand</option><option name="TL">Timor-Leste</option><option name="TG">Togo</option><option name="TK">Tokelau</option><option name="TO">Tonga</option><option name="TT">Trinidad And Tobago</option><option name="TN">Tunisia</option><option name="TR">Turkey</option><option name="TM">Turkmenistan</option><option name="TC">Turks And Caicos Islands</option><option name="TV">Tuvalu</option><option name="UG">Uganda</option><option name="UA">Ukraine</option><option name="AE">United Arab Emirates</option><option name="GB">United Kingdom</option><option name="US">United States</option><option name="UM">United States Outlying Islands</option><option name="UY">Uruguay</option><option name="UZ">Uzbekistan</option><option name="VU">Vanuatu</option><option name="VE">Venezuela</option><option name="VN">Viet Nam</option><option name="VG">Virgin Islands, British</option><option name="VI">Virgin Islands, U.S.</option><option name="WF">Wallis And Futuna</option><option name="EH">Western Sahara</option><option name="YE">Yemen</option><option name="ZM">Zambia</option><option name="ZW">Zimbabwe</option></select>

<p><button onclick="select_country();" class='btn btn-primary mt-3'>Select Country</button></p>

Javascript

function select_country() {
country_selected = document.getElementById("country_select").value;
alert(country_selected );
}