JQUERY 检查 INPUT 文本值是否为空并提示警报
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JQUERY check if INPUT text Value is empty and prompt an alert
提问by The Masta
How is it possible to display an Alert with JQUERY if i click the submit button an the value of the imput field is empty?
如果我单击提交按钮并且输入字段的值为空，如何使用 JQUERY 显示警报？
<input type="text" id="myMessage" name="shoutbox_msg" size="16" class="field_nosize" maxlength="150">
<input id="submit" type="submit" name="submit_post" class="button_nosize" value="Senden" onclick="sendMessage(); clearInput();">
回答by Tushar Gupta - curioustushar
$('#submit').click(function(){
if($('#myMessage').val() == ''){
alert('Input can not be left blank');
}
});
Update
更新
If you don't want whitespace also u can remove them using jQuery.trim()
如果你不想要空格，你也可以使用jQuery.trim()删除它们
Description: Remove the whitespace from the beginning and end of a string.
描述：删除字符串开头和结尾的空格。
$('#submit').click(function(){
if($.trim($('#myMessage').val()) == ''){
alert('Input can not be left blank');
}
});
回答by Zigri2612
Better one is here.
更好的在这里。
$('#submit').click(function()
{
if( !$('#myMessage').val() ) {
alert('warning');
}
});
And you don't necessarily need .length or see if its >0 since an empty string evaluates to false anyway but if you'd like to for readability purposes:
而且您不一定需要 .length 或查看它是否 >0 ，因为空字符串无论如何都会评估为 false 但如果您想出于可读性目的：
$('#submit').on('click',function()
{
if( $('#myMessage').val().length === 0 ) {
alert('warning');
}
});
If you're sure it will always operate on a textfield element then you can just use this.value.
如果您确定它始终对文本字段元素进行操作，那么您可以使用 this.value。
$('#submit').click(function()
{
if( !document.getElementById('myMessage').value ) {
alert('warning');
}
});
Also you should take note that $('input:text') grabs multiple elements, specify a context or use the this keyword if you just want a reference to a lone element ( provided theres one textfield in the context's descendants/children ).
此外，您应该注意 $('input:text') 抓取多个元素，指定上下文或使用 this 关键字，如果您只想引用一个单独的元素（前提是上下文的后代/子项中有一个文本字段）。
回答by Shiv Yadav
Also you can try this, if you want to focus on same text after error.
如果您想在错误后专注于相同的文本，您也可以尝试此操作。
If you wants to show this error message in a paragraph then you can use this one:
如果您想在段落中显示此错误消息，则可以使用以下内容：
$(document).ready(function () {
$("#submit").click(function () {
if($('#selBooks').val() === '') {
$("#Paragraph_id").text("Please select a book and then proceed.").show();
$('#selBooks').focus();
return false;
}
});
});
回答by Super Model
Check empty input with removing space(if user enter space) from input using trim
使用trim从输入中删除空格（如果用户输入空格）检查空输入
$(document).ready(function(){
$('#button').click(function(){
if($.trim($('#fname').val()) == '')
{
$('#fname').css("border-color", "red");
alert("Empty");
}
});
});
