javascript：检查布尔值
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javascript : checking boolean values
提问by Vinoth Kumar C M
I have a boolean value set as a hidden variable in the form and I have the below javascript .
我有一个布尔值设置为表单中的隐藏变量，我有下面的 javascript 。
$().ready(function() {
var flag = $('#popUpFlag').val();
alert("flag = "+flag);
if(flag){
alert("flag is true");
}else{
alert("flag is false");
}
})
These are the outputs for the alert .
这些是警报的输出。
flag =
flag is false
flag = false
flag is false
flag = true
flag is false
My concern is obviously the third output . When the flag is true , why is it printing "flag is false" , instead of "flag is true" . I tested it in IE8 and FF 4
我关心的显然是第三个输出。当 flag 为 true 时，为什么要打印 "flag is false" ，而不是 "flag is true" 。我在 IE8 和 FF 4 中测试过
Suggestions are welcome.
欢迎提出建议。
回答by Guffa
No, you don't have a boolean value in the hidden field. The value in the field is always a string.
不，您在隐藏字段中没有布尔值。该字段中的值始终是一个字符串。
When you use the string value as if it was a boolean value, you get unexpected results. A condition is false if the value is false, 0, ""or null, but the string "false"is neither, so it's evaluated as true.
当您像使用布尔值一样使用字符串值时，您会得到意想不到的结果。条件是假的，如果值是false，0，""或null，但是字符串"false"两者都不是，所以它作为评价true。
If you want a boolean value, you have to parse the string. An easy way is to simply check if the string has a specific value:
如果你想要一个布尔值，你必须解析字符串。一种简单的方法是简单地检查字符串是否具有特定值：
var flag = $('#popUpFlag').val() === 'true';
回答by Shadow Wizard is Ear For You
flagis a string, so have this instead:
flag是一个字符串，所以用这个代替：
if (flag === "true") {
//true
}
else if (flag === "false") {
//false
}
回答by Cyril Gupta
Hmm... I suspect that the value you are using is a string, so you're seeing the value correctly in the alert, but not when it tries to look at it like a boolean.
嗯...我怀疑您使用的值是一个字符串，所以您在警报中正确地看到了该值，但当它试图像布尔值一样查看它时则不然。
How can I convert a string to boolean in JavaScript?
Just try ocnverting to boolean and see if it still gives you the same issue
只需尝试转换为布尔值，看看它是否仍然给你同样的问题
