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Question

i have the following enum

enum EditMode {
    View = 0,
    Edit = 1,
    Delete = 2
}

Let's assume i have a variable of the enum type

var editMode = EditMode.Edit;

Why does the following code not work (goes straight to default)?

switch (editMode) {
    case EditMode.Delete:
        ...
        break;
    case EditMode.Edit:
        ...
        break;
    default:
        ...
        break;
    }

Answer 1

I also had this problem. Easy way to get around it: add a + sign before your variable in the switch, ie

switch (+editMode) {
    case EditMode.Delete:
        ...
        break;
    case EditMode.Edit:
        ...
        break;
    default:
        ...
        break;
    }

Answer 2

i have found why i does happen. somewhere in the code there is a activation function (i am using durandal) which passes this enum as a string (the function has the parameter marked as a enum but still it is a string). this is why my switch statement fails. i simply converted the value to a number and now everything works as expected. thanks anyways

Answer 3

The issue here has to do with typescript's (numeric) literal types . When you do this assignment:

var editMode = EditMode.Edit

TypeScript evaluates the type as:

var editMode: 1 = EditMode.Edit

Now, when you compare a value that typescript knows must be 1 ( EditMode.Edit ) to a value that it knows must be 0 ( EditMode.View ), it sees all this as a type-safety violation. If the variable editMode weren't an enum , typescript would merely complain, but since it's an enum , which doesn't really exist in javascript, typescript gets to control the transpilation in such a way that it actually throws an error.
So you have 2 options. So you can either coerce editMode to be a number or to be an EditMode (ie any of the values EditMode is permitted to be, not just the one assigned to editMode the variable).
Personally, I prefer to coerce it to be an EditMode , because it feels more type-safe.

To go the number route, you can do the following, which was previously mentioned:

switch(+editMode)

To go the EditMode route (which I recommend), you can pass it to a function as was mentioned, but sometimes it's a little cleaner to not write a function. If that's the case here, then you can again coerce the type in the switch statement:

switch(editMode as EditMode)

Do whichever you prefer, but I just like the clarity of explicitly saying "this variable is being treated as an EditMode " as opposed to "this variable is supposed to actually be a number , not an Enum ".

Answer 4

TypeScript version 3.7.5

this code worked for me

enum Seasons {
    Winter,
    Spring,
    Summer,
    Autum
  }

switch (+Seasons.Winter) {
    case Seasons.Winter:
        console.log('weather is cold');
        break;
    case Seasons.Spring:
        console.log('weather is spring');
        break;
    case Seasons.Summer:
        console.log('weather is summer');
        break;
    default:
        break;
}

or you can declare a constant and use as param for switch statement

const season: Seasons = Seasons.Winter
switch (+season) {
    case Seasons.Winter:
        console.log('weather is cold');
        break;
    case Seasons.Spring:
        console.log('weather is spring');
        break;
    case Seasons.Summer:
        console.log('weather is summer');
        break;
    default:
        break;
}

Answer 5

Change your EditMode enum definition to:

enum EditMode {
    View = "View",
    Edit = "Edit",
    Delete = "Delete"
}

Typescript 3.6.3

Answer 6

In case somebody else ends up here and the above options don't seem to be the issue, double-check that all of your switch statements are breaking/returning! The Typescript compiler is smart enough to see that if your case cascades through to another one, the value you're comparing on may never hit the case you expect.

let handlerName;

switch(method){
  case 'create':
    handlerName = 'createHandler';
    break;
  case 'update';
    handlerName = 'updateHandler';
    // Here is where the forgotten break would go
  default:
    throw new Error('Unrecognized Method');
}

switch(handlerName){
  case 'createHandler':
    ...
    break;
  case 'updateHandler':
    // You will see an error on this case because
    // the compiler knows that execution will never
    // arrive here with handler === 'updateHandler'
  default:
    throw new Error('Unrecognized Handler');
}

Answer 7

Use it like this.

const enum OperationsType{
    CREATE="CREATE",
    DELETE="DELETE",
    UPDATE="UPDATE"
}

Answer 8

With //@ts-ignore suppress you can do:

//@ts-ignore
switch (EditMode[editMode] as EditMode) {
    case EditMode.Delete:
        ...
        break;
    case EditMode.Edit:
        ...
        break;
    default:
        ...
        break;
    }
}

Answer 9

如果枚举是在单独的打字稿文件中定义的，请确保它标有“导出”，并且您在引用它的打字稿文件的顶部正确导入它。

Answer 10

If you use the switch expression in a function with typed parameter, this works as expected.

Example:

enum EditMode {
    View,
    Edit,
    Delete,
}

function testSwitch(editMode: EditMode) {
    switch(editMode) {
        case EditMode.Delete:
            console.log("delete");
            break;
        case EditMode.Edit:
            console.log("edit");
            break;
        default:
            console.log("default");
            break;
    }
}

testSwitch(EditMode.Edit)

will compile 🥳 and output edit 👍

Answer 11

In my case I had the switch inside a condition, which was coercing the enum into a value:

enum A {
    VAL_A,
    VAL_B,
    VAL_C
}
interface ia {
    maybe?: A
}
const o: ia = {maybe: 0}
if(o.maybe){ //<-- o.maybe is not falsey (thus, is not 0)
    switch(o.maybe) {
        case A.VAL_A: //<-- Error! we know that o.maybe is not 0. Its VAL_B | VAL_C
        break;
    }

}

Answer 12

Declare your enum using const :

const enum EditMode {
    View = 0,
    Edit = 1,
    Delete = 2
}