I'm a rather newbie for TypeScript.
Can anyone explain the meaning of this TypeScript code snippet?
function MappableMixin<T extends Constructor<Model<MappableTraits>>>(Base: T) {
Code link is here
Thanks.
CodePudding user response:
Let's break this down bit by bit:
function MappableMixin(Base: T)
The function takes a generic type T
a its argument
function MappableMixin<T extends Something>(Base: T)
The <TypeArgument>
term just between the function name and the (params)
term tells typescript to expect that the return type of this function of of type TypeArgument
. In the case that TypeArgument
is of the form T extends Something
, it means that the returned value will be a type that extends Something
, meaning it has all the properties of Something
. Essentially in this case, MappableMixin
takes in some argument, and returns that argument with the extra properties of the type Something
.
<Model<MappableTraits>>
This is a generic type with a type argument. So for example, you may have a type Model
, which accepts a type as an argument:
interface Model<T> {
thing1: string;
thing2: T
}
In the case of using <Model<MappableTraits>>
, Model<T>
would have the type
interface Model<MappableTraits> {
thing1: string;
thing2: MappableTraits
}
So Constructor<Model<MappableTraits>>>
follows this same pattern, just 2 layers deep.
So the whole phrase means that MappableMixin
is a function that returns an extended version of the value you gave it. The extension is specifically of the type Constructor<Model<MappableTraits>>>
, which is a 2-layer typescript generic.