Typescript：可以使用enum作为函数参数类型吗？

Question

Simple question, yet I have a doubt and couldn't find the answer.

Suppose you have this enum:

export enum fooEnum {
    Foo = 'foo',
    Bar = 'bar'
}

Then would it be ok to type my function parameters this way? Meaning 'I expect to receive a string 'foo' or 'bar' as parameter and expect to return 'foo' or 'bar'

function doStuff(myParam: FooEnum): FooEnum {
    return myParam;
};

Answer 1

It is perfectly fine to use an enum as parameter.

The only thing that you might want to consider (but in most cases negligible), is that an enum will be included in the generated JavaScript .

export enum fooEnum {
    Foo = 'foo',
    Bar = 'bar'
}

Will generate the following JavaScript code (or similar):

var fooEnum;
(function (fooEnum) {
    fooEnum["Foo"] = "foo";
    fooEnum["Bar"] = "bar";
})(fooEnum || (fooEnum = {}));

As an alternative you could use a String Literal type, which will not be included in the generated code.

export type fooType = 'foo' | 'bar';

---

EDIT - Thanks to Aleksey L.

You can also define a const enum , which is also not included in the generated code.

export const enum fooEnum {
    Foo = 'foo',
    Bar = 'bar'
}

And when used

var bar = fooEnum.Bar;

the following code will be generated as

var b = 'bar';

const enum VS string literal type

With the const enum approach it comes down to just personal preference whether you find

doStuff(fooEnum.Bar);

or string literal types

doStuff('bar');

more readable. The generated result will be the same in both cases.

Answer 2

An enum is just like any other type it can be used as a parameter and also used as a return type. So yes that syntax would work fine.

I do not know why you would need to pass in an Enum value and then return a different Enum value but none the less you can do what you are doing and it is correct in TypeScript.