javascript - JavaScript 元素验证

Question

我想检查是否已使用 javascript 选择了我的多个下拉列表中的任何内容。

<select name="id" id="id" size=22 multiple >

并且如果任何复选框已被选中

<input type="checkbox" name="inst" class="asa" value="inst1"> 
<input type="checkbox" name="inst" class="asa" value="inst2">

Answer 1

试试这个代码

演示

var selectVal = document.getElementById('id');
var selectCount = 0;
var values = [];
for (var i = 0; i < selectVal.options.length; i++) {
  if (selectVal.options[i].selected) {
    selectCount++;
    values.push(selectVal.options[i].value);
  }
}

对于复选框

<input type="checkbox" name="inst" class="asa" id="check1" value="inst1"> 
<input type="checkbox" name="inst" class="asa" id="check2" value="inst2">

var check1 = document.getElementById("check1").checked;
alert(check1);
var check2 = document.getElementById("check2").checked;
alert(check2);

Answer 2

尝试

var select = document.getElementById('id');

var selected  = [];
for(var i =0 ; i < select.options.length; i++){
    if(select.options[i].selected){
        selected.push(select.options[i].value);
    }
}
if(selected.length == 0){
    alert('not selected');
}

演示：小提琴

Answer 3

HTML：

<select name="id" id="three" size=22 multiple>
    <option value="thevalue">Option</option>
</select>

<select name="id" id="four" size=22 multiple>
    <option value="thevalue" selected="selected">Option</option>
</select>

JS：

var one = document.getElementById("one");
var two = document.getElementById("two");
var three = document.getElementById("three");

if(one.checked)
    console.log("one = checked!");
else
    console.log("one != checked");

if(two.checked)
    console.log("two = checked!");
else
    console.log("two != checked");

if(three.value)
    console.log("something is selected in three!");
else
    console.log("nothing is selected in three");

if(four.value)
    console.log("something is selected in four!");
else
    console.log("nothing is selected in four");

小提琴覆盖复选框和选择。

显然，这是一个非常冗长的示例，但您可以将其删减以删除您需要的内容。