I have a variable and I want to set the variable as typescript type annotations.
type mytype = "image1" | "image2" | "image3"
images: mytype;
That is no problem, but I want to generate the mytype from an Array. How is that possible?
images = ["image1", "image2", "image3"]
mytype = images.map(i => '"' + i + '"').join(' | ')
Do you think like this?
const images = ["image1", "image2", "image3"] as const;
type mytype = typeof images[number]; // mytype is now "image1" | "image2" | "image3"
I would use an enum for this case, unfortunately I don't think you can create the type on the fly based on dynamic values (or if you should, it defeats the purpose of ts).
https://www.typescriptlang.org/docs/handbook/enums.html
enum Images {
ImageType1 = 'image1',
ImageType2 = 'image2',
...
};
const values = Object.values(Images); // will be an array ['image1', 'image2', ...];
// use as a type
const foo = (image: Images) => {
// do stuff, "image" will be restricted to 'image1' | 'image2' | ... values
}
There are two options to tell Typescript you want to assign an array to a variable:
1. Using the [] operator
The easiest and best way is to use [] after your type
type mytype = "image1" | "image2" | "image3"
images: mytype[];
2. Casting a type to an Array
type mytype = "image1" | "image2" | "image3"
images: Array<mytype>;