CODEWITHSUNDEEP
javascriptenumsswitch-statementcase
Shivan Dragon
Shivan Dragon

Reputation: 15229

JavaScript switch case using enum

I have an "enum" declared like so:

var PlaceType = {
        PASSABLE_TERRAIN: 1,
        IMPASSABLE_TERRAIN: 0,
        SOMEWHAT_PASSABLE_TERRAIN: 2,
        PATH: 3
    };

and a function declared like this:

setPlaceType(placeType) {
        this.clear = false;
        this.placeType = placeType;

        alert("before switch "+(PlaceType.SOMEWHAT_PASSABLE_TERRAIN==this.placeType));
        switch(this.placeType) {
        case PlaceType.PASSABLE_TERRAIN: {
            alert("Case PASSABLE");
            break;
        }
        case PlaceType.IMPASSABLE_TERRAIN: {
            alert("Case IMPASSABLE");
            break;
        }
        case PlaceType.SOMEWHAT_PASSABLE_TERRAIN: {
            alert("Case SOMEWHAT_PASSABLE");
            break;
        }
        case PlaceType.PATH: {
            alert("Case PATH");
            break;
        }
        default: {
            alert("case default");
        }
        }
    }

if I call it like this:

setPlaceType(1);

I get the following alerts: "before switch true", "case default"

if I call it like this:

setPlaceType(2);

I get the following alerts: "before switch false", "case default"

In other words, the function is called with the proper argument, which, when doing (what it seems to me to be) the same comparison as the switch but via "==" I get correct behavior, but the switch never matches the values to the appropriate case. Does anybody know why?

Upvotes: 12

Views: 33804

Answers (5)

David L
David L

Reputation: 723

Another way to use enum for switch case:

   const PlaceType = Object.freeze({
            PASSABLE_TERRAIN: 1,
            IMPASSABLE_TERRAIN: 0,
            SOMEWHAT_PASSABLE_TERRAIN: 2,
            PATH: 3
        });

   function setPlaceType(placeType){
      return({
              0:"Case IMPASSABLE_TERRAIN",
              1:"Case PASSABLE_TERRAIN",
              2:"Case SOMEWHAT_PASSABLE_TERRAIN",
              3:"PATH"      
              }[placeType]);
     }

Upvotes: 2

jbabey
jbabey

Reputation: 46657

The comparison operator will cast both operands to strings if either operator is a string. If you pass in a string, you are comparing string == number which will cast the number to a string and, in the case of passing the string '2', it will be true.

switch case comparison uses the identity operator === and will fail if the operands are not the same type.

long story short, make sure you are always passing a number if your cases are comparing against numbers, you can double check like this:

setPlaceType(placeType) {
    if (typeof placeType !== 'number') {
        throw new Error('You must pass a number to setPlaceType!');
    }
    ...
}

also, you should be calling your function like this:

setPlaceType(PlaceType.PASSABLE_TERRAIN);

otherwise there's not really any point to using the "enumeration" (i use that term loosely) object.

Upvotes: 9

epascarello
epascarello

Reputation: 207527

The matching case is determined using the === identity operator, not the == equality operator. The expressions must match without any type conversion. It would fail if you are passing in a string and not an integer.

setPlaceType(1);  //"Case PASSABLE"
setPlaceType("1");  //"case default"

Example running your code with the above lines: jsFiddle

So if you are saying it is failing, you are probably comparing a string to a number. Use parseInt.

this.placeType = parseint(placeType,10);

Upvotes: 1

bPratik
bPratik

Reputation: 7018

When you are doing the comparison using == js is using type-coercion to cast the 2 operands to an intermediate type, string in this case, and thus compare them successfully.

So to get the effect to work with your switch statement, you will need to cast as such

this.placeType = parseint(placeType);

What you also got to learn here is that it is not really an ideal practice to compare 2 values in javascript using the == operator, instead use the === operator which also checks for the types to be the same. So in your case,

alert("before switch "+(PlaceType.SOMEWHAT_PASSABLE_TERRAIN==this.placeType));

would have failed if you would have used === as you are comparing an int and string

Working demo here: http://jsfiddle.net/pratik136/ATx8c/

Upvotes: 1

user1585121
user1585121

Reputation:

Refering to this => Switch-Case for strings in Javascript not working as expected

Switch do a ===, while if do a ==.

Hope this help! have a nice day

Upvotes: 1

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