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.

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 { __1 } = resolveTypes(code);
        expect(__1).to.equal("{ a: number; b: string; }");
    });

    it("resolveTypes also works with template literals", () => {
        const { __2 } = resolveTypes`
            type ${1} = Pick<{ a: number; b: string; c: any; }, 'a' | 'b'>;
            type ${2} = Pick<${1}, 'a'>;
        `;
        expect(__2).to.equal("{ a: number; }");
    });
});

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 declaration and returns these as strings in a JavaScript object. 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.

resolveTypes ignores any compilation errors, but may return "<unknown>" for any types it cannot resolve.

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

TODOS

• generalize parameter names & positions
• handle non-intrinsic types correctly
• correctly extract compilation options
• allow injecting options
• comment this code
• write readme
• tests
• Automate prettification, test running, etc
• make npm library out of this
• blog post
• return possible compilation errors from resolveTypes