jQuery - 简单的输入验证 - “空”和“非空”
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jQuery - simple input validation - "empty" and "not empty"
提问by Wordpressor
I have an input that I want to validate:
我有一个要验证的输入：
<input type="text" id="input" />
And here's the JS:
这是JS：
jQuery("#input").live('change', function() {
if("#input:not(:empty)") {
alert('not empty');
}
else if("#input:empty") {
alert('empty');
}
});
Even when the "#input" is empty there's no way of displaying alert with "empty" message. So, basically, no matter what I do, only the first statement is true and the second is false, always.
即使“#input”为空，也无法显示带有“空”消息的警报。所以，基本上，无论我做什么，总是只有第一个陈述是正确的，第二个陈述是错误的。
What's wrong?
怎么了？
回答by Gordon Gustafson
JQuery's :empty selectorselects all elements on the page that are empty in the sense that they have no child elements, including text nodes, not all inputs that have no text in them.
JQuery 的 :empty 选择器选择页面上所有空元素，因为它们没有子元素，包括文本节点，而不是所有没有文本的输入。
Jquery: How to check if an input element has not been filled in.
Here's the code stolen from the above thread:
这是从上述线程中窃取的代码：
$('#apply-form input').blur(function() //whenever you click off an input element
{
if( !$(this).val() ) { //if it is blank.
alert('empty');
}
});
This works because an empty string in JavaScript is a 'falsy value', which basically means if you try to use it as a boolean value it will always evaluate to false. If you want, you can change the conditional to $(this).val() === ''for added clarity. :D
这是有效的，因为 JavaScript 中的空字符串是一个“假值”，这基本上意味着如果您尝试将它用作布尔值，它将始终评估为false. 如果需要，您可以将条件更改为$(this).val() === ''以增加清晰度。:D
回答by Jason Gennaro
You could do this
你可以这样做
$("#input").blur(function(){
if($(this).val() == ''){
alert('empty');
}
});
http://jsfiddle.net/jasongennaro/Y5P9k/1/
http://jsfiddle.net/jasonennaro/Y5P9k/1/
When the input has lost focusthat is .blur(), then check the value of the #input.
当输入丢失时focus，即.blur()检查 的值#input。
If it is empty == ''then trigger the alert.
如果它是空的，== ''则触发警报。
回答by Willem
jQuery("#input").live('change', function() {
// since we check more than once against the value, place it in a var.
var inputvalue = $("#input").attr("value");
// if it's value **IS NOT** ""
if(inputvalue !== "") {
jQuery(this).css('outline', 'solid 1px red');
}
// else if it's value **IS** ""
else if(inputvalue === "") {
alert('empty');
}
});
回答by Mcloide
Actually there is a simpler way to do this, just:
其实有一个更简单的方法来做到这一点，只是：
if ($("#input").is('empty')) {
console.log('empty');
} else {
console.log('not empty');
}
