Javascript 如何检查表单输入是否有价值
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How to check if form input has value
提问by Choy
I'm trying to check if a form input has any value (doesn't matter what the value is) so that I can append the value to the action URL on submit if it does exist. I need to add the name of the param before adding the value, and just leaving a blank param name like "P=" without any value messes up the page.
我正在尝试检查表单输入是否有任何值（与值无关），以便我可以在提交时将该值附加到操作 URL（如果它确实存在）。我需要在添加值之前添加参数的名称，并且只留下一个空白的参数名称，例如“P=”而没有任何值会弄乱页面。
Here's my code:
这是我的代码：
function getParam() {
// reset url in case there were any previous params inputted
document.form.action = 'http://www.domain.com'
if (document.getElementById('p').value == 1) {
document.form.action += 'P=' + document.getElementById('p').value;
}
if (document.getElementbyId('q').value == 1) {
document.form.action += 'Q=' + document.getElementById('q').value;
}
}
and the form:
和形式：
<form name="form" id="form" method="post" action="">
<input type="text" id="p" value="">
<input type="text" id="q" value="">
<input type="submit" value="Update" onClick="getParam();">
</form>
I thought setting value == 1 would do a simple exists, doesn't exist check regardless of what the submitted value was, but I guess I'm wrong.
我认为设置 value == 1 会做一个简单的存在，不存在检查无论提交的值是什么，但我想我错了。
Also, I'm using if statements, but I believe that's bad code, since I don't have an else. Perhaps, using a switch statement, though I'm not sure how I would set that up. Perhaps:
另外，我正在使用 if 语句，但我认为这是糟糕的代码，因为我没有 else。也许，使用 switch 语句，尽管我不确定如何设置。也许：
switch(value) {
case document.getElementById('p').value == 1 :
document.form.action += 'P=' + document.getElementById('p').value; :
case document.getElementById('q').value == 1 :
document.form.action += 'Q=' + document.getElementById('q').value; break;
}
回答by N 1.1
var val = document.getElementById('p').value;
if (/^\s*$/.test(val)){
//value is either empty or contains whitespace characters
//do not append the value
}
else{
//code for appending the value to url
}
P.S.: Its better than checking against value.lengthbecause ' '.length= 3.
PS：它比检查更好，value.length因为' '.length= 3。
