The "Assert signatures" feature looks excellent. The biggest issue with typescript has always been validating external inputs actually meet the type contracts that your code says they do. With this, it looks like this could be written as library!
interface ContactInfo {
address_1: string;
address_2?: string;
city: string;
state: string;
zip: string;
phone: number;
}
function isContactInfo(arg: any): arg is ContactInfo {
let valid = false;
const contactInfoFields: { readonly [key: string]: string[] } = {
address_1: [ 'string', ],
address_2: [ 'string', 'undefined' ],
city: [ 'string', ],
state: [ 'string', ],
zip: [ 'string', ],
phone: [ 'number' ],
};
if (typeof arg !== 'object') {
return valid;
}
for (const key in contactInfoFields) {
if(!contactInfoFields[key].includes(typeof arg[key]) || arg[key] === '' || Number.isNaN(arg[key])) {
return valid;
}
}
valid = true;
return valid;
}- io-ts[1]
This requires you to write your types as a runtime value, and allows you to extract static types from those, e.g.:
const ContactInfo = t.type({
address_1: t.string,
...
})
type ContactInfo = t.TypeOf<typeof ContactInfo>
Note that we can have the same name for the type and value because they live in different namespaces. When you do ContactInfo.decode, you're calling the decode property of `const ContactInfo`. When you use `ContactInfo` in a type position (e.g. `function x(arg: ContactInfo)`), you're using the `type ContactInfo` declaration
- typescript-is[2]
This uses TypeScript's transformer API. You can use it with https://github.com/cevek/ttypescript. It generates validators for your interfaces/types/etc at compile-time.
type TypeOf<T> = (x: any) => x is (infer U) ? U : never;
import { number, optional, record, string, TypeOf } from 'narrows';
const isContactInfo = record({
address_1: string,
address_2: optional(string),
city: string,
state: string,
zip: string,
phone: number
})
type ContactInfo = TypeOf<typeof isContactInfo>;
Typescript-is looks like it might have an overall edge, though, because we can use it on the autogenerated types as well with almost no hassle.
instanceof
typeof
Array.isArray()
== null