给定更正的 HTML，添加了id属性和label元素，为各种表单元素提供额外的点击目标：
<input type="checkbox" id="input1" name="events" value="event01" />
<label for="input1">Event 01</label>
<br/>
<input type="checkbox" id="input2" name="events" value="event02" />
<label for="input2">Event 02</label>
<select name="selectOne">
<option value="00" selected="selected">00</option>
<option value="01">01</option>
<option value="02">02</option>
<option value="03">03</option>
<option value="04">04</option>
<option value="05">05</option>
<option value="06">06</option>
<option value="07">07</option>
</select>
<br/>
<input type="text" name="displayTxtBox" id="displayTxtBox" size="10" maxlength="50" value="" />
以下 JavaScript 似乎适用于您的预期结果，尽管我并不完全确定您的意图：
function showAmount(el, selectEl, targetEl, clearOnUncheck) {
/* the following is an optional, Boolean, variable, so a ternary
conditional is used, which checks that 'clearOnUncheck' exists,
if it does then the variable is assigned its own value,
if *not* then it's explicitly assigned the value of false
note it's Boolean, *not* a string: don't quote this value */
var clearOnUncheck = clearOnUncheck ? clearOnUncheck : false;
if (!el || !selectEl || !targetEl) {
// sanity checking, these are *required* arguments for the function
return false;
}
// if the checkbox is checked, continue
else if (el.checked) {
/* assigning the conditions I'm testing to variables, so if conditions
change they only have to be changed in one place */
var index = selectEl.selectedIndex,
textcontent = (typeof(el.textContent) != 'undefined');
if (textcontent) {
// up-to-date browsers
/* sets the value of the text-input to be the string contained
within the selected option from the select element */
targetEl.value = selectEl
.getElementsByTagName('option')[index]
.textContent;
}
else if (window.innerText) {
// IE < 8
// as above, but uses innerText for IE
targetEl.value = selectEl
.getElementsByTagName('option')[index]
.innerText;
}
}
/* if the checkbox is unchecked, and you've set the Boolean for the
optional clearOnUncheck to true (remember, *not* a string, don't quote) */
else if (!el.checked && clearOnUncheck) {
/* if clearOnUncheck is true, the value is cleared from the text-input,
if clearOnUncheck is set to false, or not-set, the text-box value
persists after unchecking the checkbox */
targetEl.value = '';
}
}
// references to the elements
var input2 = document.getElementById('input2'),
select = document.getElementsByName('selectOne')[0],
textInput = document.getElementById('displayTxtBox');
// binding the function to the onchange event of the input2 and selectOne elements.
input2.onchange = function() {
showAmount(input2, select, textInput, true);
};
select.onchange = function() {
/* because the clearOnUncheck argument depends on the changing of the
checkbox there's no point in passing it to the showAmount() function
in the select's onchange event-handler */
showAmount(input2, select, textInput);
};
JS Fiddle 演示clearOnUncheck == true
JS Fiddle 演示clearOnUncheck == false
clearOnUncheck未设置的 JS Fiddle 演示
参考：