在Javascript中检查文本框是否为空 [英] Checking if a textbox is empty in Javascript
问题描述
这是我的代码,如果文本框留空,它应该引发 alert
消息:
函数a(id)
{
var n = document.getElementById(id).value;
if(n.length< 1)
{
window.alert(Field is blank);
返回false;
}
}
我得到的错误是字段是第一次没有得到验证 onChange
。但是,当文本框中填充了一些数据并被删除时,现在 OnChange
被触发,并且显示 alert
消息。如何修复这个bug?
onchange
文本框的值与之前的值相比发生了变化,所以第一次它不起作用,因为状态没有改变。
所以它是更好地使用 onblur
事件或提交表单。
函数checkTextField(field){document.getElementById(error)。innerText =(field.value ===)? 领域是空的。 :Field is filled。;}
< input type =textonblur =checkTextField(this); />< p id =error>< / p>
$ b
This is my code which was supposed to raise an alert
message if the textbox is left empty:
function a(id)
{
var n=document.getElementById(id).value;
if (n.length < 1)
{
window.alert("Field is blank");
return false;
}
}
The bug I'm getting is that the field is not getting verified onChange
the first time. But when the text box is filled with some data and erased, now the OnChange
fires, and the alert
message is displayed. How can I fix this bug?
onchange
will work only if the value of the textbox changed compared to the value it had before, so for the first time it won't work because the state didn't change.
So it is better to use onblur
event or on submitting the form.
function checkTextField(field) {
document.getElementById("error").innerText =
(field.value === "") ? "Field is empty." : "Field is filled.";
}
<input type="text" onblur="checkTextField(this);" />
<p id="error"></p>
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