如何创建 - 在输入字段上创建自动完成

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) {
  /* autocomplete 自动完成功能有两个参数，
  文本字段元素和一组可能的自动完成值:*/
  var currentFocus;
  /*当有人在文本字段中写入时执行一个函数:*/
  inp.addEventListener("input", function(e) {
      var a, b, i, val = this.value;
      /*关闭任何已经打开的自动完成值列表*/
      closeAllLists();
      if (!val) { return false;}
      currentFocus = -1;
      /*创建一个包含项目（值）的 DIV 元素:*/
      a = document.createElement("DIV");
      a.setAttribute("id", this.id + "autocomplete-list");
      a.setAttribute("class", "autocomplete-items");
      /*将 DIV 元素附加为自动完成容器的子元素:*/
      this.parentNode.appendChild(a);
      /*对于数组中的每一项...*/
      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一个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);
          /*插入将保存当前数组项的值的输入字段:*/
          b.innerHTML += "<input type='hidden' value='" + arr[i] + "'>";
          /*当有人点击项目值（DIV元素）时执行一个函数:*/
              b.addEventListener("click", function(e) {
              /*插入自动完成文本字段的值:*/
              inp.value = this.getElementsByTagName("input")[0].value;
              /*关闭自动完成值的列表，
              （或任何其他打开的自动完成值列表:*/
              closeAllLists();
          });
          a.appendChild(b);
        }
      }
  });
  /*执行一个函数按下键盘上的一个键:*/
  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，
        增加 currentFocus 变量:*/
        currentFocus++;
        /*并使当前项目更加可见:*/
        addActive(x);
      } else if (e.keyCode == 38) { //up
        /*如果按下向上箭头键，
        减少 currentFocus 变量:*/
        currentFocus--;
        /* 并使当前项目更明显:*/
        addActive(x);
      } else if (e.keyCode == 13) {
        /*如果按下 ENTER 键，则阻止提交表单，*/
        e.preventDefault();
        if (currentFocus > -1) {
          /*并模拟点击 "active" 项:*/
          if (x) x[currentFocus].click();
        }
      }
  });
  function addActive(x) {
    /*一个将项目分类为 "active" 的函数:*/
    if (!x) return false;
    /*首先删除所有项目的 "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) {
    /*从所有自动完成项中删除 "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，
    除了作为参数传递的那个:*/
    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]);
    }
  }
}
/*当有人点击文档时执行一个函数:*/
document.addEventListener("click", function (e) {
    closeAllLists(e.target);
});
}