javascript 如果条件为假，则防止默认
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If conditions false then prevent default
提问by esafwan
I have a link. When some one clicks on that I want to check some conditions before letting it work. If it's falsethe default action should be prevented.
我有一个链接。当有人点击它时，我想在让它工作之前检查一些条件。如果false是默认操作，则应阻止。
$(".pager-next a.active").click(function(event) {
if (!a == 1) {
event.preventDefault();
}
});
The link should only work if ais equal to 1. Is the above code correct. ais set to 1if a particular condition is met. The link should only work if the condition is met.
该链接仅在a等于时才有效1。上面的代码是否正确。如果满足特定条件，a则设置为1。该链接仅在满足条件时才有效。
回答by Rory McCrossan
Assuming by 'should only work if a is equal to 1' you mean the text of the aelement is equal to 1, try this:
假设 '应该只在 a 等于 1 时起作用，你的意思是a元素的文本等于 1，试试这个：
$(".pager-next a.active").click(function(event) {
if ($(this).text() != "1") {
event.preventDefault();
}
});
You can amend text()to use whichever attribute of the element is available to you in jQuery.
您可以修改text()以使用 jQuery 中可用的元素的任何属性。
UPDATE
更新
my a is a var which hold the value 0 until a condition is met.
我的 a 是一个 var ，它保持值 0 直到满足条件。
In which case, the problem was simply that your equality operator was incorrect:
在这种情况下，问题只是您的相等运算符不正确：
$(".pager-next a.active").click(function(event) {
if (a != 1) {
event.preventDefault();
}
});
回答by Thomas Clayson
Be careful:
当心：
!aevaluates to true or false. If a conversion of ato a bool is truethen !aevaluates to false.
!a评估为真或假。如果转换为abooltrue则!a评估为 false。
All positive integers evaluate to true. So !awill evaluate to false. A comparison using double equals ==to 1 will test that boolean !awith the boolean 1or true. So if ais a positive integer as I suspect it is then your ifstatement will ALWAYS evaluate to false.
所有正整数的计算结果为true。所以!a将评估为假。使用 double 等于==1 的比较将使用布尔!a值1or测试该布尔值true。因此，如果a是我怀疑的正整数，那么您的if陈述将始终评估为假。
If you want to test is something is NOT something else you need to change the first equals in your comparison operator (===) to be a !.
如果您想测试某个东西不是别的东西，您需要将比较运算符 ( ===) 中的第一个等号更改为 a !。
E.g. var a = 2; if(a!==1) { // do something }<-- A is 2 and therefore the if comparison wille evaluate to true as adoes notequal 1.
例如var a = 2; if(a!==1) { // do something }<-- A 是 2，因此 if 比较将评估为 truea不等于1。
In your code we have:
在您的代码中，我们有：
var a = 2;
if(!a==1){
// a was 2 (or boolean true by default)
// but using ! has negated its boolean value
// so !a evaluates to boolean false
// which is being compared to 1 (evaluating to boolean true)
// so this if statement will never get here
}
Hope that helps
希望有帮助
P.S. Remember your comparison operators:
PS 记住你的比较运算符：
!"hello world" == 0 // true
!"hello world" === 0 // false
Update
更新
I saw your comment on another post which said that ais 0until something happens then it is 1.
我看到了另一个帖子里面说，您的评论a是0，直到事情发生那么它是1。
In this case:
在这种情况下：
var a = 0; // integer 0 or bool false
if(!a==1){ // if the bool opposite of 0 (false) is equal to 1 (true)
// well, opposite of false is true, so you're checking if true is equal to true
// so this will get called
e.preventDefault();
}
