resolve-types

resolve-types allows you to resolve types in inline code. This functionality is handy to write unit tests for type operators and check them in a regular test suite.

Compatibility Note

The shape of the return type of resolveTypes changed in version 0.2.0 to return diagnostic errors. It now returns a value of shape { diagnostics, types } whereas it returned the content of types directly in versions 0.1.*.

Example

resolve-types can be used as follows to test type operators:

import "jest"; // example test runner
import { resolveTypes } from "resolve-types";
 
describe("Type Operators Example", () => {
    it("Pick extracts keys from objects", () => {
        const code = "\
            type __1 = Pick<{ a: number; b: string; c: any; }, 'a' | 'b'>;\
        ";
        const { types: { __1 } } = resolveTypes(code);
        expect(__1).to.equal("{ a: number; b: string; }");
    });
 
    it("resolveTypes also works with template literals", () => {
        const { types: { __2 } } = resolveTypes`
            type ${1} = Pick<{ a: number; b: string; c: any; }, 'a' | 'b'>;
            type ${2} = Pick<${1}, 'a'>;
        `;
        expect(__2).to.equal("{ a: number; }");
    });
 
    it("resolveTypes returns diagnostic messages in the 'diagnostics' property ", () => {
        const { diagnostics, types } = resolveTypes`
            import * as foo from 'i-dont-exist';
        `;
        expect(diagnostics[0].code).toEqual(2307);
        expect(diagnostics[0].messageText).toEqual("Cannot find module 'i-dont-exist'.");
    });
});

Documentation

The resolve-types library exposes two functions: resolveTypes which does the actual work and setOptions which allows setting options for the TypeScript compilation.

resolveTypes

resolveTypes takes either a string or a template literal, creates a TypeScript program out of it and extracts the types of specially named type declarations and returns compliation diagnostics and the resolved types. Type type declarations must have the form type __[a-zA-Z0-9][_a-zA-Z0-9]*. In template literals, any expressions which are resolved are automatically prefixed with __ to fulfill the naming requirement.

The return value of resolveTypes has the shape

{
    types: { [key: string]: string; };
    diagnostics: ts.Diagnostic[];
}

where ts.Diagnostic is the type of Diagnostics from the TypeScript compiler. Both types and diagnostics are computed lazily to minimize the performance impact of objects which are never read.

resolveTypes may return "<unknown>" for any types it cannot resolve. This happens especially for compilation errors, check the diagnostics property for these.

setOptions

setOptions allows setting TypeScript compiler options before compiling the program with resolveTypes. By default, the options from the project's tsconfig.json will be used. To override this, set setOptions second parameter to true.

setOptions sets a global options variable, so its use is stateful and will be maintained across invocations of resolveTypes.

Contributing

Contributions in the form of bug reports, change requests, documentation and code changes are welcome. Please make sure there is an outstanding ticket which has been discussed before making large code changes.

License

MIT