Typescript enum switch not working
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
(i.e. 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
".
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;
}
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
I also had this problem. Easy way to get around it: add a +
sign before your variable in the switch, i.e.
switch (+editMode) {
case EditMode.Delete:
...
break;
case EditMode.Edit:
...
break;
default:
...
break;
}