variant/lib/lookup.js

Variant types (a.k.a. Discriminated Unions) in TypeScript

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
exports.partialLookup = exports.lookup = void 0;
/**
 * Process an unknown variant by comparing it to a provided lookup table and returning the proper result.
 * @param obj some object that extends `{[K]: string}`.
 * @param handler a lookup table going from the various keys of `obj`'s type to any.
 * @param typeKey the key used as the discriminant.
 */
function lookup(obj, handler, typeKey) {
    const typeString = obj[typeKey !== null && typeKey !== void 0 ? typeKey : 'type'];
    return handler[typeString];
}
exports.lookup = lookup;
/**
 * Process an unknown variant by comparing it to a provided lookup table and returning the proper result.
 * If the handler does not account for the case, returns undefined
 * @param obj some object that extends `{[K]: string}`.
 * @param handler a partial lookup table going from some keys of `obj`'s type to any.
 * @param typeKey the key used as the discriminant.
 */
function partialLookup(obj, handler, typeKey) {
    // Takes advantage of the fact that handler with missing keys will return undefined.
    return lookup(obj, handler, typeKey);
}
exports.partialLookup = partialLookup;
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