Switch case with conditions

Am I writing the correct switch case with conditions?

var cnt = $("开发者_如何学运维;#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!

A switch works by comparing what is in switch() to every case.

switch (cnt) {
    case 1: ....
    case 2: ....
    case 3: ....
}

works like:

if (cnt === 1) ...
if (cnt === 2) ...
if (cnt === 3) ...

Therefore, you can't have any logic in the case statements.

switch (cnt) {
    case (cnt >= 10 && cnt <= 20): ...
}

works like

if (cnt === (cnt >= 10 && cnt <= 20)) ...

and that's just nonsense. :)

Use if () { } else if () { } else { } instead.

You should not use switch for this scenario. This is the proper approach:

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');
}

This should work with this :

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');
            }

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 if statements.

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.

$('.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');
        }
    }); ` 

What you are doing is to look for (0) or (1) results.

(cnt >= 10 && cnt <= 20) returns either true or false.

--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--

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;
}

Switch case is every help full instead of if else statement :

     switch ($("[id*=btnSave]").val()) {
        case 'Search':
            saveFlight();
            break;
        case 'Update':
            break;
        case 'Delete':
            break;
        default:
            break;
    }

Ok it is late but in case you or someone else still want to you use a switch or simply have a better understanding of how the switch statement works.

What was wrong is that your switch expression should match in strict comparison one of your case expression. If there is no match it will look for a default. You can still use your expression in your case with the && operator that makes Short-circuit evaluation.

Ok you already know all that. For matching the strict comparison you should add at the end of all your case expression && cnt.

Like follow:

switch(mySwitchExpression)
case customEpression && mySwitchExpression: StatementList
.
.
.
default:StatementList

var cnt = $("#div1 p").length;
alert(cnt);
switch (cnt) {
case (cnt >= 10 && cnt <= 20 && cnt):
    alert('10');
    break;
case (cnt >= 21 && cnt <= 30 && cnt):
    alert('21');
    break;
case (cnt >= 31 && cnt <= 40 && cnt):
    alert('31');
    break;
default:
    alert('>41');
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div id="div1">
<p> p1</p>
<p> p2</p>
<p> p3</p>
<p> p3</p>
<p> p4</p>
<p> p5</p>
<p> p6</p>
<p> p7</p>
<p> p8</p>
<p> p9</p>
<p> p10</p>
<p> p11</p>
<p> p12</p>
</div>