10

I have problem in some JavaScript that I am writing where the Switch statement does not seem to be working as expected.

switch (msg.ResultType) {
  case 0:
    $('#txtConsole').val("Some Val 0");
    break;
  case 1:
    $('#txtConsole').val("Some Val 1");
    break;
  case 2:
    $('#txtConsole').text("Some Val 2");
    break;
}

The ResultType is an integer value 0-2 and I can see that in FireBug. In all cases, the switch transfers control to the final break statement which means all the logic is completely skipped. What am I missing?

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7 Answers 7

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19

I'm sure that a switch uses === for comparison in Actionscript and since JS and AS both follow the ECMAScript standard, I guess the same applies to JS. My guess is that the value is not actually a Number, but perhaps a String.

You could try to use parseInt(msg.ResultType) in the switch or use strings in the cases.

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6 Comments

ALWAYS specify the second parameter to parseInt! It's the radix, so likely you'll want: parseInt(msg.ResultType, 10); If you don't supply it, it will try to guess the radix and horrible things will happen.
Well, horrible things will only happen if you pass something like 077, which will be interpreted as octal (but no 078, for example), or 0x10, but in the second case it's rather clear that you have base 16. Anyway, adding the radix explicitly won't hurt, so it's not a bad idea either.
In this case the radix is not necessary, although I have used it just for clarity and completeness. I am not someone who believes terse code is the best code. The values coming in are defined in an enumeration on the server side and so will never be in some non-standard format.
078 will be interpreted as octal as well: parseInt("078") returns 7. parseInt("08") returns 0. These can be the source of nearly impossible to find bugs.
Sorry for being misleading, I tested it only in AS, where parseInt seems to be implemented in a slightly different way than in JS (so parseInt("078") returns 78 ).
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2

I ran into a similar problem and the issue turned out to be that where as it was showing as an int value, the switch statement was reading it as a string variable. May not be the case here, but that is what happened to me.

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Comments

2

Try this:

switch (msg.ResultType-0) {
  case 0:
    $('#txtConsole').val("Some Val 0");
  break;
  case 1:
    $('#txtConsole').val("Some Val 1");
  break;
  case 2:
    $('#txtConsole').text("Some Val 2");
  break;
}

The -0 will force (coerce) it to treating your value as an integer without changing the value, and it's much shorter than parseInt.

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3 Comments

This is one of those answers that is slick, but not as explanatory as using parseInt.
And presumably, Javascript will just be calling parseInt behind the scenes, so all we are saving is a bit of typing.
Tried this and it did not work. I still ended up with the original problem. The parseInt (with and without radix) worked reliably.
0

Are you sure the ResultType is an integer (e.g. 0) and not a string (e.g. "0")?

This could easily explain the difference in behaviour

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1 Comment

It was definitely an integer according to FireBug. Not that it is the definitive source, but a pretty good indicator.
0

It looks like changing it to parseInt(msg.ResultType) has forced the JavaScript engine to properly treat it as an integer. Thanks for the help.

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Comments

0

First thing I noticed is that in two of the three cases, you're calling .val() and in the third you're calling .text().

If you tried changing the case statements to strings instead of ints, then the only thing I can think of is that you're hitting an exception somewhere along the line possibly caused by accessing an undefined variable.

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0

Probably the most powerful coercion to int available in ES5 is: 

     msg.ResultType | 0

This is one of the foundation stones on which asm.js resides. This leads to very optimised ES5 and is used by compiling on presence of: 

    "use asm"

directive (in FF and Chromium). This coercion results in Int32 type being used for Numbers in ES5 that do represent an "int". So the cook-book recipe solution for the original question from 5 years ago is this:

 "use strict" ;
$("#txtConsole").val(
  switch (msg.ResultType | 0) {
     case 0:
          "Some Val 0";
     break;
    case 1:
         "Some Val 1";
    break;
    case 2:
         "Some Val 2";
    break;
    default :
         "Illegal ResultType";
  });
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