如何在单击时更改文本字段的值

<input type="button" name="insert" value="0" style="width: 30px; height: 35px" onClick="zeroCheck()">

function zeroCheck(){
    if (entry.value == '0'){
        entry.value=='0';
    } else{
        return entry.value+='0';
    }
}

我能想到的最简单的解决方案是:

function zeroCheck(el) {
    // caching the value because it's used multiple times
    var v = el.value;
    /* setting the value with a ternary/conditional operator:
       v == '0' : testing that the value is equal to the given string
       if it is equal: the value is set to: '' + v (so there's no change),
       if it is not equal: the value is set to: '0' + v (so a zero is prepended).
    */
    el.value = ( v == '0' ? '' : '0' ) + v;
}

JS Fiddle demo.

在链接的演示中，上面的JavaScript与以下HTML一起使用:

<input type="button" name="insert" value="0" onClick="zeroCheck(this)" />
<input type="button" name="insert" value="1" onClick="zeroCheck(this)" />
<input type="button" name="insert" value="2" onClick="zeroCheck(this)" />
<input type="button" name="insert" value="3" onClick="zeroCheck(this)" />

添加一些(基本的)错误处理:

function zeroCheck(el) {
    // caching the value, because we're using it a few times
    var v = el.value,
    // saving the number (this way 1.4 and 1 are both preserved)
        num = parseFloat(v);
    // a basic check to see that the value is a number
    // (or rather that it is 'not Not-a-Number):
    if (!isNaN(num)) {
        el.value = ( v == '0' ? '' : '0' ) + v;
    }
    else {
        // default handling here, to handle non-numeric values:
        el.value = 0;
    }
}

JS Fiddle demo.

因为我认为我误解了这个问题，我用另一种可能性更新了这个答案，它处理兄弟文本输入元素，并且还考虑到已经具有前导零的值:

function zeroCheck(el) {
    /* gets all the 'input' elements within the same parentNode that
       contains the button that's to be clicked: */
    var inputs = el.parentNode.getElementsByTagName('input'),
    /* declaring the variables to be used in the loop, so they're not
       being constantly re-declared through the loop */
        v, num;
    for (var i = 0, len = inputs.length; i < len; i++) {
        v = inputs[i].value;
        num = parseFloat(v);
        // if the input is the button, don't do anything, just keep going
        if (inputs[i] == el) {
            continue;
        // otherwise if the number is not Not-a-Number:
        } else if (!isNaN(num)) {
            inputs[i].value = (v.charAt(0) == '0' ? '' : '0') + v;
        } else {
            inputs[i].value = 0; // error-handling
        }
    }
}

JS提琴演示

好了，因为这和我想象的有很大的不同，让我们把这里弄清楚，让我们简化这个过程。如果函数在PHP中，你将无法设置，甚至无法获得，input控件的值。在PHP文件中，您需要做这样的事情(请注意，我假设form是POST ):

$entryVal = $_POST["entry"];
$newEntryVal = "0";
if (trim($entryVal) != "0") {
    $newEntryVal = $newEntryVal + "0";
}

，然后在后面的标记中:

<input type="text" name="entry" size="20" value = "<?= $newEntryVal ?>">

最好给你的输入一个id:

<input type="button" id="someid" name="insert" value="0" style="width: 30px; height: 35px" onClick="zeroCheck()">
function zeroCheck(){
var entry = document.getElementById("someid");
    if (entry.value == '0'){
       entry.value = '0';
   } else {
      entry.value += '0';
   }
}

有很多东西是缺失的。下面是正确的代码:

function zeroCheck(){
var entry = document.getElementsByName("entry")[0];
    if (entry.value == '0'){
       entry.value = parseInt('0');
   } else {
      entry.value += parseInt('0');
   }
}

不需要返回，您正在使用==，因为应该是=来赋值。还有一个问题是你想用entry.value += '0';代码做什么