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我在JavaScript中爲我的文本框在aspx頁面中創建自動選項卡功能。當我試圖專注於下一個文本框時,我收到一條錯誤消息 "Unable to get property 'focus' of undefined or null reference"
。文本框在javascript中爲空或未定義
<asp:TextBox type="text" ID="areaCodeTextBox" runat="server" MaxLength="3" size="1" onkeypress="return isNumberKey(event)" onkeyup="Tab(this, 'exchangeTextBox')" />
<asp:TextBox type="text" ID="exchangeTextBox" runat="server" MaxLength="3" size="1" onkeypress="return isNumberKey(event)" onkeyup="Tab(this, 'suffixTextBox')"/>
<asp:TextBox type="text" ID="suffixTextBox" runat="server" MaxLength="4" size="2" onkeypress="return isNumberKey(event)" />
<SCRIPT language=Javascript>
function isNumberKey(evt)
{
var charCode = (evt.which) ? evt.which : evt.keyCode;
if (charCode > 31 && (charCode < 48 || charCode > 57))
return false;
return true;
}
function Tab(fromTextBox, toTextBox) {
// Determine if the current field's max length has been reached.
var length = fromTextBox.value.length;
var maxLength = fromTextBox.getAttribute("maxLength");
if (length == maxLength) {
// Retreive the next field in the tab sequence, and give it the focus.
document.getElementById(toTextBox).focus();
}
}
</SCRIPT>
有什麼明顯的,我做錯了我調用焦點方法的方式嗎?
編輯*我沒有直接在JavaScript中引用文本框,我試圖將ID作爲參數傳遞。這會對文本框爲什麼會返回爲空作出改變嗎?
可能的複製[的document.getElementById ('id').aspx失敗的ASP.net javascript函數](https://stackoverflow.com/questions/9101904/document-getelementbyidid-value-failing-in-asp-net-javascript-function) –