Javascript 有条件的切换案例
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Switch case with conditions
提问by Jasl
Am I writing the correct switch case?
我写的是正确的开关盒吗？
var cnt = $("#div1 p").length;
alert(cnt);
switch (cnt) {
case (cnt >= 10 && cnt <= 20):
alert('10');
break;
case (cnt >= 21 && cnt <= 30):
alert('21');
break;
case (cnt >= 31 && cnt <= 40):
alert('31');
break;
default:
alert('>41');
}
For some reason, the alert does not occur when the conditions are matched!
由于某种原因，当条件匹配时不会发生警报！
采纳答案by rochal
You should not use switchfor this scenario. This is the proper approach:
您不应该switch在这种情况下使用。这是正确的方法：
var cnt = $("#div1 p").length;
alert(cnt);
if (cnt >= 10 && cnt <= 20)
{
alert('10');
}
else if (cnt >= 21 && cnt <= 30)
{
alert('21');
}
else if (cnt >= 31 && cnt <= 40)
{
alert('31');
}
else
{
alert('>41');
}
回答by deceze
A switch works by comparing what is in switch()to every case.
开关的工作原理是比较switch()每个case.
switch (cnt) {
case 1: ....
case 2: ....
case 3: ....
}
works like:
像这样工作：
if (cnt == 1) ...
if (cnt == 2) ...
if (cnt == 3) ...
Therefore, you can't have any logic in the case statements.
因此，在 case 语句中不能有任何逻辑。
switch (cnt) {
case (cnt >= 10 && cnt <= 20): ...
}
works like
像
if (cnt == (cnt >= 10 && cnt <= 20)) ...
and that's just nonsense. :)
那只是胡说八道。:)
Use if () { } else if () { } else { }instead.
使用if () { } else if () { } else { }来代替。
回答by Fabien Ménager
This should work with this :
这应该适用于：
var cnt = $("#div1 p").length;
switch (true) {
case (cnt >= 10 && cnt <= 20):
alert('10');
break;
case (cnt >= 21 && cnt <= 30):
alert('21');
break;
case (cnt >= 31 && cnt <= 40):
break;
default:
alert('>41');
}
回答by Pete Robie
Something I came upon while trying to work a spinner was to allow for flexibility within the script without the use of a ton of ifstatements.
我在尝试使用微调器时遇到的事情是允许脚本中的灵活性，而无需使用大量if语句。
Since this is a simpler solution than iterating through an array to check for a single instance of a class present it keeps the script cleaner. Any suggestions for cleaning the code further are welcome.
由于这是比遍历数组以检查存在的类的单个实例更简单的解决方案，因此可以使脚本更清晰。欢迎任何进一步清理代码的建议。
$('.next').click(function(){
var imageToSlide = $('#imageSprite'); // Get id of image
switch(true) {
case (imageToSlide.hasClass('pos1')):
imageToSlide.removeClass('pos1').addClass('pos2');
break;
case (imageToSlide.hasClass('pos2')):
imageToSlide.removeClass('pos2').addClass('pos3');
break;
case (imageToSlide.hasClass('pos3')):
imageToSlide.removeClass('pos3').addClass('pos4');
break;
case (imageToSlide.hasClass('pos4')):
imageToSlide.removeClass('pos4').addClass('pos1');
}
}); `
回答by jAndy
What you are doing is to look for (0) or (1) results.
您正在做的是寻找 (0) 或 (1) 结果。
(cnt >= 10 && cnt <= 20) returns either true or false.
(cnt >= 10 && cnt <= 20) 返回真或假。
--edit-- you can't use case with boolean (logic) experessions. The statement cnt >= 10 returns zero for false or one for true. Hence, it will we case(1) or case(0) which will never match to the length.--edit--
--edit--您不能使用带有布尔（逻辑）表达式的 case。语句 cnt >= 10 为 false 返回 0，为 true 返回 1。因此，我们将永远不会与长度匹配的 case(1) 或 case(0) 。- 编辑 -
回答by Waqar Ahmed
function date_conversion(start_date){
var formattedDate = new Date(start_date);
var d = formattedDate.getDate();
var m = formattedDate.getMonth();
var month;
m += 1; // JavaScript months are 0-11
switch (m) {
case 1: {
month="Jan";
break;
}
case 2: {
month="Feb";
break;
}
case 3: {
month="Mar";
break;
}
case 4: {
month="Apr";
break;
}
case 5: {
month="May";
break;
}
case 6: {
month="Jun";
break;
}
case 7: {
month="Jul";
break;
}
case 8: {
month="Aug";
break;
}
case 9: {
month="Sep";
break;
}
case 10: {
month="Oct";
break;
}
case 11: {
month="Nov";
break;
}
case 12: {
month="Dec";
break;
}
}
var y = formattedDate.getFullYear();
var now_date=d + "-" + month + "-" + y;
return now_date;
}
回答by hariomthapa.in
Switch case is every help full instead of if else statement :
Switch case 是所有帮助，而不是 if else 语句：
switch ($("[id*=btnSave]").val()) {
case 'Search':
saveFlight();
break;
case 'Update':
break;
case 'Delete':
break;
default:
break;
}
