Question

我有一个文本区域，我为用户键入了250个字符的限制。这很好用。我添加了一些代码来动态编辑该框。是否可以构造“编辑”代码来限制框，所以只有250个字符与初始添加框相同？

下面是添加框：

JSP ：

<td colspan="3">
    You have <strong><span id="commentsCounter">${const['COMMENT_MAX_LENGTH']}</span></strong> characters left.<br/>
    <textarea id="comment" name="comment" rows="3"
        onfocus="characterCounter('commentsCounter',${const['COMMENT_MAX_LENGTH']}, this)"
        onkeydown="characterCounter('commentsCounter',${const['COMMENT_MAX_LENGTH']}, this)"
        onkeyup="characterCounter('commentsCounter',${const['COMMENT_MAX_LENGTH']}, this)"></textarea>
        <a href="javascript:addComment();"><img src="../images/icon_add.gif" border="0" alt="Add"/></a>
</td>

的javascript ：

    function characterCounter(id, maxLen, inputElement)
{
    spanId = document.getElementById(id);

    if (spanId)
    {
        // Update the counter the user sees.
        var whatIsLeft = maxLen - inputElement.value.length;

        if ( whatIsLeft < 0 ) whatIsLeft = 0;
        spanId.innerText = whatIsLeft;
    }

    // Restrict user from entering more than the maxlen.
    if ( inputElement.value.length > maxLen )
    {
        inputElement.value = inputElement.value.substring( 0, maxLen );
    }
}

下面是用于编辑该框的片段代码....我如何在下面构建镜像以反映上面的javascript只是为了阻止该框输入超过250个字符？

    function editCommentToggle( id )
{
    theRow = document.getElementById("id"+id);
    //user = theRow.cells[0].innerHTML;
    //date = theRow.cells[1].innerHTML;
    com = theRow.cells[2].innerHTML;


    idx = 2;


        // Comment field

        cell = theRow.cells[idx];
        while( cell.childNodes.length > 0 ) cell.removeChild(cell.childNodes[0]);
        element = document.createElement("textarea");
        element.id="comments-"+id;
        element.rows="3";
        element.value = com;
        element.style.width =  "400px";
        element.maxLength="250";
        cell.appendChild(element);

刚添加：

maxlength = 250;
element.onfocus = element.onkeydown = element.onkeyup = function(){return characterCounterEdit(undefined, maxlength, element);}; 
        cell.appendChild(element);

 function characterCounterEdit(id, maxLen, inputElement)
{
    spanId = document.getElementById(id);

    if (spanId)
    {
        // Update the counter the user sees.
        var whatIsLeft = maxLen - inputElement.value.length;

        if ( whatIsLeft < 0 ) whatIsLeft = 0;
        spanId.innerText = whatIsLeft;
    }

    // Restrict user from entering more than the maxlen.
    if ( inputElement.value.length > maxLen )
    {
        inputElement.value = inputElement.value.substring( 0, maxLen );
    }
}

现在我得到了：

'value.length'为null或不是对象

Answer 1

...
element.maxLength="250";
//add this
element.onfocus = element.onkeydown = element.onkeyup = function(){return characterCounter(undefined, 250, element);};
//end add
cell.appendChild(element);
...

javascript textarea限制问题

1 个答案: