How TO - Autocomplete

var countries = ["Afghanistan","Albania","Algeria","Andorra","Angola","Anguilla","Antigua & Barbuda","Argentina","Armenia","Aruba","Australia","Austria","Azerbaijan","Bahamas","Bahrain","Bangladesh","Barbados","Belarus","Belgium","Belize","Benin","Bermuda","Bhutan","Bolivia","Bosnia & Herzegovina","Botswana","Brazil","British Virgin Islands","Brunei","Bulgaria","Burkina Faso","Burundi","Cambodia","Cameroon","Canada","Cape Verde","Cayman Islands","Central Arfrican Republic","Chad","Chile","China","Colombia","Congo","Cook Islands","Costa Rica","Cote D Ivoire","Croatia","Cuba","Curacao","Cyprus","Czech Republic","Denmark","Djibouti","Dominica","Dominican Republic","Ecuador","Egypt","El Salvador","Equatorial Guinea","Eritrea","Estonia","Ethiopia","Falkland Islands","Faroe Islands","Fiji","Finland","France","French Polynesia","French West Indies","Gabon","Gambia","Georgia","Germany","Ghana","Gibraltar","Greece","Greenland","Grenada","Guam","Guatemala","Guernsey","Guinea","Guinea Bissau","Guyana","Haiti","Honduras","Hong Kong","Hungary","Iceland","India","Indonesia","Iran","Iraq","Ireland","Isle of Man","Israel","Italy","Jamaica","Japan","Jersey","Jordan","Kazakhstan","Kenya","Kiribati","Kosovo","Kuwait","Kyrgyzstan","Laos","Latvia","Lebanon","Lesotho","Liberia","Libya","Liechtenstein","Lithuania","Luxembourg","Macau","Macedonia","Madagascar","Malawi","Malaysia","Maldives","Mali","Malta","Marshall Islands","Mauritania","Mauritius","Mexico","Micronesia","Moldova","Monaco","Mongolia","Montenegro","Montserrat","Morocco","Mozambique","Myanmar","Namibia","Nauro","Nepal","Netherlands","Netherlands Antilles","New Caledonia","New Zealand","Nicaragua","Niger","Nigeria","North Korea","Norway","Oman","Pakistan","Palau","Palestine","Panama","Papua New Guinea","Paraguay","Peru","Philippines","Poland","Portugal","Puerto Rico","Qatar","Reunion","Romania","Russia","Rwanda","Saint Pierre & Miquelon","Samoa","San Marino","Sao Tome and Principe","Saudi Arabia","Senegal","Serbia","Seychelles","Sierra Leone","Singapore","Slovakia","Slovenia","Solomon Islands","Somalia","South Africa","South Korea","South Sudan","Spain","Sri Lanka","St Kitts & Nevis","St Lucia","St Vincent","Sudan","Suriname","Swaziland","Sweden","Switzerland","Syria","Taiwan","Tajikistan","Tanzania","Thailand","Timor L'Este","Togo","Tonga","Trinidad & Tobago","Tunisia","Turkey","Turkmenistan","Turks & Caicos","Tuvalu","Uganda","Ukraine","United Arab Emirates","United Kingdom","United States of America","Uruguay","Uzbekistan","Vanuatu","Vatican City","Venezuela","Vietnam","Virgin Islands (US)","Yemen","Zambia","Zimbabwe"];

function autocomplete(inp, arr) {
  /*此自动完成函数接受两个参数，
  文本字段元素和一个可能的自动完成值的数组：*/
  var currentFocus;
  /*当有人在文本字段中输入内容时执行函数：*/
  inp.addEventListener("input", function(e) {
      var a, b, i, val = this.value;
      /*关闭任何已打开的自动完成值列表*/
      closeAllLists();
      if (!val) { return false;}
      currentFocus = -1;
      /*创建将包含项目（值）的 DIV 元素：*/
      a = document.createElement("DIV");
      a.setAttribute("id", this.id + "autocomplete-list");
      a.setAttribute("class", "autocomplete-items");
      /*将 DIV 元素作为自动完成容器的子项追加：*/
      this.parentNode.appendChild(a);
      /*对于数组中的每个项目...*/
      for (i = 0; i < arr.length; i++) {
        /*检查项目是否以与文本字段值相同的字母开头：*/
        if (arr[i].substr(0, val.length).toUpperCase() == val.toUpperCase()) {
          /*为每个匹配的元素创建 DIV 元素：*/
          b = document.createElement("DIV");
          /*将匹配的字母加粗：*/
          b.innerHTML = "<strong>" + arr[i].substr(0, val.length) + "</strong>";
          b.innerHTML += arr[i].substr(val.length);
          /*插入一个 input 字段，其中将保存当前数组项的值：*/
          b.innerHTML += "<input type='hidden' value='" + arr[i] + "'>";
          /*当有人单击项目值（DIV 元素）时执行函数：*/
              b.addEventListener("click", function(e) {
              /*为自动完成文本字段插入值：*/
              inp.value = this.getElementsByTagName("input")[0].value;
              /*关闭自动完成值列表，
              （或任何其他打开的自动完成值列表：*/
              closeAllLists();
          });
          a.appendChild(b);
        }
      }
  });
  /*当有人在键盘上按下按键时执行函数：*/
  inp.addEventListener("keydown", function(e) {
      var x = document.getElementById(this.id + "autocomplete-list");
      if (x) x = x.getElementsByTagName("div");
      if (e.keyCode == 40) {
        /*如果按下箭头 DOWN 键，
        则增加 currentFocus 变量：*/
        currentFocus++;
        /*并使当前项目更加可见：*/
        addActive(x);
      } else if (e.keyCode == 38) { // up
        /*如果按下箭头 UP 键，
        则减少 currentFocus 变量：*/
        currentFocus--;
        /*并使当前项目更加可见：*/
        addActive(x);
      } else if (e.keyCode == 13) {
        /*如果按下 ENTER 键，则阻止表单提交，*/
        e.preventDefault();
        if (currentFocus > -1) {
          /*然后模拟单击“活动”项目：*/
          if (x) x[currentFocus].click();
        }
      }
  });
  function addActive(x) {
    /*一个将项目分类为“活动”的函数：*/
    if (!x) return false;
    /*首先从所有项目中删除“active”类：*/
    removeActive(x);
    if (currentFocus >= x.length) currentFocus = 0;
    if (currentFocus < 0) currentFocus = (x.length - 1);
    /*添加类“autocomplete-active”：*/
    x[currentFocus].classList.add("autocomplete-active");
  }
  function removeActive(x) {
    /*一个从所有自动完成项目中删除“active”类的函数：*/
    for (var i = 0; i < x.length; i++) {
      x[i].classList.remove("autocomplete-active");
    }
  }
  function closeAllLists(elmnt) {
    /*关闭文档中的所有自动完成列表，
    排除作为参数传递的列表：*/
    var x = document.getElementsByClassName("autocomplete-items");
    for (var i = 0; i < x.length; i++) {
      if (elmnt != x[i] && elmnt != inp) {
      x[i].parentNode.removeChild(x[i]);
    }
  }
}
/*当有人在文档中单击时执行函数：*/
document.addEventListener("click", function (e) {
    closeAllLists(e.target);
});
}