使用javascript自动选择自定义选择框中的第一个选项

Question

我试图创建一个自定义的选择框，但是我找到了一个不错的网站，提供了符合我要求的必要代码。 但是代码中缺少一件事，那就是当我单击下拉框时自动选择列表中的第一个选项。 换句话说，我希望单击箭头时突出显示列表中的第一项。 如果有人可以帮助我将此功能添加到代码中，我将不胜感激。

我在其中找到代码的站点来自W3Schools，链接为

https://www.w3schools.com/howto/tryit.asp?filename=tryhow_custom_select

提前致谢！

的HTML

---

    <div class="custom-select" style="width:200px;">
  <select>
    <option value="0">Select car:</option>
    <option value="1">Audi</option>
    <option value="2">BMW</option>
    <option value="3">Citroen</option>
    <option value="4">Ford</option>
    <option value="5">Honda</option>
    <option value="6">Jaguar</option>
    <option value="7">Land Rover</option>
    <option value="8">Mercedes</option>
    <option value="9">Mini</option>
    <option value="10">Nissan</option>
    <option value="11">Toyota</option>
    <option value="12">Volvo</option>
  </select>
</div>

的CSS

---

/*the container must be positioned relative:*/
.custom-select {
  position: relative;
  font-family: Arial;
}
.custom-select select {
  display: none; /*hide original SELECT element:*/
}
.select-selected {
  background-color: DodgerBlue;
}
/*style the arrow inside the select element:*/
.select-selected:after {
  position: absolute;
  content: "";
  top: 14px;
  right: 10px;
  width: 0;
  height: 0;
  border: 6px solid transparent;
  border-color: #fff transparent transparent transparent;
}
/*point the arrow upwards when the select box is open (active):*/
.select-selected.select-arrow-active:after {
  border-color: transparent transparent #fff transparent;
  top: 7px;
}
/*style the items (options), including the selected item:*/
.select-items div,.select-selected {
  color: #ffffff;
  padding: 8px 16px;
  border: 1px solid transparent;
  border-color: transparent transparent rgba(0, 0, 0, 0.1) transparent;
  cursor: pointer;
}
/*style items (options):*/
.select-items {
  position: absolute;
  background-color: DodgerBlue;
  top: 100%;
  left: 0;
  right: 0;
  z-index: 99;
}
/*hide the items when the select box is closed:*/
.select-hide {
  display: none;
}
.select-items div:hover, .same-as-selected {
  background-color: rgba(0, 0, 0, 0.1);
}

Java脚本

---

var x, i, j, selElmnt, a, b, c;
/*look for any elements with the class "custom-select":*/
x = document.getElementsByClassName("custom-select");
for (i = 0; i < x.length; i++) {
  selElmnt = x[i].getElementsByTagName("select")[0];
  /*for each element, create a new DIV that will act as the selected item:*/
  a = document.createElement("DIV");
  a.setAttribute("class", "select-selected");
  a.innerHTML = selElmnt.options[selElmnt.selectedIndex].innerHTML;
  x[i].appendChild(a);
  /*for each element, create a new DIV that will contain the option list:*/
  b = document.createElement("DIV");
  b.setAttribute("class", "select-items select-hide");
  for (j = 1; j < selElmnt.length; j++) {
    /*for each option in the original select element,
    create a new DIV that will act as an option item:*/
    c = document.createElement("DIV");
    c.innerHTML = selElmnt.options[j].innerHTML;
    c.addEventListener("click", function(e) {
        /*when an item is clicked, update the original select box,
        and the selected item:*/
        var y, i, k, s, h;
        s = this.parentNode.parentNode.getElementsByTagName("select")[0];
        h = this.parentNode.previousSibling;
        for (i = 0; i < s.length; i++) {
          if (s.options[i].innerHTML == this.innerHTML) {
            s.selectedIndex = i;
            h.innerHTML = this.innerHTML;
            y = this.parentNode.getElementsByClassName("same-as-selected");
            for (k = 0; k < y.length; k++) {
              y[k].removeAttribute("class");
            }
            this.setAttribute("class", "same-as-selected");
            break;
          }
        }
        h.click();
    });
    b.appendChild(c);
  }
  x[i].appendChild(b);
  a.addEventListener("click", function(e) {
      /*when the select box is clicked, close any other select boxes,
      and open/close the current select box:*/
      e.stopPropagation();
      closeAllSelect(this);
      this.nextSibling.classList.toggle("select-hide");
      this.classList.toggle("select-arrow-active");
  });
}
function closeAllSelect(elmnt) {
  /*a function that will close all select boxes in the document,
  except the current select box:*/
  var x, y, i, arrNo = [];
  x = document.getElementsByClassName("select-items");
  y = document.getElementsByClassName("select-selected");
  for (i = 0; i < y.length; i++) {
    if (elmnt == y[i]) {
      arrNo.push(i)
    } else {
      y[i].classList.remove("select-arrow-active");
    }
  }
  for (i = 0; i < x.length; i++) {
    if (arrNo.indexOf(i)) {
      x[i].classList.add("select-hide");
    }
  }
}
/*if the user clicks anywhere outside the select box,
then close all select boxes:*/
document.addEventListener("click", closeAllSelect);

Answer 1

为了在默认情况下在下拉列表中选择一个选项，您要做的就是将selected属性应用于所需的<option> 。 例如，

<option value="1" selected>Audi</option>

可以在以下内容中看到：

 var x, i, j, selElmnt, a, b, c; /*look for any elements with the class "custom-select":*/ x = document.getElementsByClassName("custom-select"); for (i = 0; i < x.length; i++) { selElmnt = x[i].getElementsByTagName("select")[0]; /*for each element, create a new DIV that will act as the selected item:*/ a = document.createElement("DIV"); a.setAttribute("class", "select-selected"); a.innerHTML = selElmnt.options[selElmnt.selectedIndex].innerHTML; x[i].appendChild(a); /*for each element, create a new DIV that will contain the option list:*/ b = document.createElement("DIV"); b.setAttribute("class", "select-items select-hide"); for (j = 1; j < selElmnt.length; j++) { /*for each option in the original select element, create a new DIV that will act as an option item:*/ c = document.createElement("DIV"); c.innerHTML = selElmnt.options[j].innerHTML; c.addEventListener("click", function(e) { /*when an item is clicked, update the original select box, and the selected item:*/ var y, i, k, s, h; s = this.parentNode.parentNode.getElementsByTagName("select")[0]; h = this.parentNode.previousSibling; for (i = 0; i < s.length; i++) { if (s.options[i].innerHTML == this.innerHTML) { s.selectedIndex = i; h.innerHTML = this.innerHTML; y = this.parentNode.getElementsByClassName("same-as-selected"); for (k = 0; k < y.length; k++) { y[k].removeAttribute("class"); } this.setAttribute("class", "same-as-selected"); break; } } h.click(); }); b.appendChild(c); } x[i].appendChild(b); a.addEventListener("click", function(e) { /*when the select box is clicked, close any other select boxes, and open/close the current select box:*/ e.stopPropagation(); closeAllSelect(this); this.nextSibling.classList.toggle("select-hide"); this.classList.toggle("select-arrow-active"); }); } function closeAllSelect(elmnt) { /*a function that will close all select boxes in the document, except the current select box:*/ var x, y, i, arrNo = []; x = document.getElementsByClassName("select-items"); y = document.getElementsByClassName("select-selected"); for (i = 0; i < y.length; i++) { if (elmnt == y[i]) { arrNo.push(i) } else { y[i].classList.remove("select-arrow-active"); } } for (i = 0; i < x.length; i++) { if (arrNo.indexOf(i)) { x[i].classList.add("select-hide"); } } } /*if the user clicks anywhere outside the select box, then close all select boxes:*/ document.addEventListener("click", closeAllSelect); 

 /*the container must be positioned relative:*/ .custom-select { position: relative; font-family: Arial; } .custom-select select { display: none; /*hide original SELECT element:*/ } .select-selected { background-color: DodgerBlue; } /*style the arrow inside the select element:*/ .select-selected:after { position: absolute; content: ""; top: 14px; right: 10px; width: 0; height: 0; border: 6px solid transparent; border-color: #fff transparent transparent transparent; } /*point the arrow upwards when the select box is open (active):*/ .select-selected.select-arrow-active:after { border-color: transparent transparent #fff transparent; top: 7px; } /*style the items (options), including the selected item:*/ .select-items div, .select-selected { color: #ffffff; padding: 8px 16px; border: 1px solid transparent; border-color: transparent transparent rgba(0, 0, 0, 0.1) transparent; cursor: pointer; } /*style items (options):*/ .select-items { position: absolute; background-color: DodgerBlue; top: 100%; left: 0; right: 0; z-index: 99; } /*hide the items when the select box is closed:*/ .select-hide { display: none; } .select-items div:hover, .same-as-selected { background-color: rgba(0, 0, 0, 0.1); } 

 <div class="custom-select" style="width:200px;"> <select> <option value="0">Select car:</option> <option value="1" selected>Audi</option> <option value="2">BMW</option> <option value="3">Citroen</option> <option value="4">Ford</option> <option value="5">Honda</option> <option value="6">Jaguar</option> <option value="7">Land Rover</option> <option value="8">Mercedes</option> <option value="9">Mini</option> <option value="10">Nissan</option> <option value="11">Toyota</option> <option value="12">Volvo</option> </select> </div> 

Answer 2

希望有帮助，请尝试禁用“选择汽车”元素

<option value="0" disabled>Select car:</option>

Answer 3

您可以将所选内容放入选项<option value="1" selected>Audi</option>这将是默认选择。