如何检查表单输入是否有值 [英] How to check if form input has value

问题描述

我正在尝试检查表单输入是否有任何值（与值是什么无关），以便我可以将值附加到提交时的操作URL（如果它存在）。我需要在添加值之前添加参数的名称，只留下一个空白的参数名称，如P =，没有任何值会弄乱页面。

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.

这里是我的代码：

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;
    }

}

和表格：

<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>

我认为设定值== 1会做一个简单的存在，不存在检查无论什么提交的值是，但我想我错了。

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.

另外，我正在使用if语句，但我认为这是错误的代码，因为我没有别的。也许，使用switch语句，虽然我不确定如何设置它。也许：

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:

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;
}

推荐答案

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
}

PS：它比检查 value.length 更好，因为''。length = 3。

P.S.: Its better than checking against value.length because ' '.length = 3.

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