php - 如何在单击时更改文本字段的值？

Question

我正在用 PHP 制作一个计算器。我一直遇到的一个问题是这个。

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

所以有一个仅包含“0”的文本字段，我希望它只用另一个零替换那个零，而不是在上面添加另一个“0”。

我的文本框名称叫做 entry。

为了解决这个问题，我尝试开发了这个功能，但没有成功。

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

这根本没有做任何事情。我在这里做错了什么？

如果有人能提供帮助，我们将不胜感激。

Answer 1

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 .

因为我认为我误读了这个问题，所以我用另一种可能性更新了这个答案，它处理同级文本输入元素并且还考虑了已经有前导零的值:

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 Fiddle demo .