Zod playground - Conditional object fields based on value of other field

package.json

{
  "name": "zod",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "type": "module",
  "scripts": {
    "init": "tsc --init",
    "start": "node --loader ts-node/esm index.ts"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "devDependencies": {
    "ts-node": "^10.9.1",
    "typescript": "^5.1.6"
  },
  "dependencies": {
    "zod": "^3.21.4"
  }
}

tsconfig.json

{
  "compilerOptions": {
    /* Visit https://aka.ms/tsconfig to read more about this file */
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    // "tsBuildInfoFile": "./.tsbuildinfo",              /* Specify the path to .tsbuildinfo incremental compilation file. */
    // "disableSourceOfProjectReferenceRedirect": true,  /* Disable preferring source files instead of declaration files when referencing composite projects. */
    // "disableSolutionSearching": true,                 /* Opt a project out of multi-project reference checking when editing. */
    // "disableReferencedProjectLoad": true,             /* Reduce the number of projects loaded automatically by TypeScript. */
    /* Language and Environment */
    "target": "es2022", /* Set the JavaScript language version for emitted JavaScript and include compatible library declarations. */
    // "lib": [],                                        /* Specify a set of bundled library declaration files that describe the target runtime environment. */
    // "jsx": "preserve",                                /* Specify what JSX code is generated. */
    // "experimentalDecorators": true,                   /* Enable experimental support for legacy experimental decorators. */
    // "emitDecoratorMetadata": true,                    /* Emit design-type metadata for decorated declarations in source files. */
    // "jsxFactory": "",                                 /* Specify the JSX factory function used when targeting React JSX emit, e.g. 'React.createElement' or 'h'. */
    // "jsxFragmentFactory": "",                         /* Specify the JSX Fragment reference used for fragments when targeting React JSX emit e.g. 'React.Fragment' or 'Fragment'. */
    // "jsxImportSource": "",                            /* Specify module specifier used to import the JSX factory functions when using 'jsx: react-jsx*'. */
    // "reactNamespace": "",                             /* Specify the object invoked for 'createElement'. This only applies when targeting 'react' JSX emit. */
    // "noLib": true,                                    /* Disable including any library files, including the default lib.d.ts. */
    // "useDefineForClassFields": true,                  /* Emit ECMAScript-standard-compliant class fields. */
    // "moduleDetection": "auto",                        /* Control what method is used to detect module-format JS files. */
    /* Modules */
    "module": "ES2022", /* Specify what module code is generated. */
    // "rootDir": "./",                                  /* Specify the root folder within your source files. */
    "moduleResolution": "Node", /* Specify how TypeScript looks up a file from a given module specifier. */
    // "baseUrl": "./",                                  /* Specify the base directory to resolve non-relative module names. */
    // "paths": {},                                      /* Specify a set of entries that re-map imports to additional lookup locations. */
    // "rootDirs": [],                                   /* Allow multiple folders to be treated as one when resolving modules. */
    // "typeRoots": [],                                  /* Specify multiple folders that act like './node_modules/@types'. */
    // "types": [],                                      /* Specify type package names to be included without being referenced in a source file. */
    // "allowUmdGlobalAccess": true,                     /* Allow accessing UMD globals from modules. */
    // "moduleSuffixes": [],                             /* List of file name suffixes to search when resolving a module. */
    // "allowImportingTsExtensions": true,               /* Allow imports to include TypeScript file extensions. Requires '--moduleResolution bundler' and either '--noEmit' or '--emitDeclarationOnly' to be set. */
    // "resolvePackageJsonExports": true,                /* Use the package.json 'exports' field when resolving package imports. */
    // "resolvePackageJsonImports": true,                /* Use the package.json 'imports' field when resolving imports. */
    // "customConditions": [],                           /* Conditions to set in addition to the resolver-specific defaults when resolving imports. */
    // "resolveJsonModule": true,                        /* Enable importing .json files. */
    // "allowArbitraryExtensions": true,                 /* Enable importing files with any extension, provided a declaration file is present. */
    // "noResolve": true,                                /* Disallow 'import's, 'require's or '<reference>'s from expanding the number of files TypeScript should add to a project. */
    /* JavaScript Support */
    // "allowJs": true,                                  /* Allow JavaScript files to be a part of your program. Use the 'checkJS' option to get errors from these files. */
    // "checkJs": true,                                  /* Enable error reporting in type-checked JavaScript files. */
    // "maxNodeModuleJsDepth": 1,                        /* Specify the maximum folder depth used for checking JavaScript files from 'node_modules'. Only applicable with 'allowJs'. */
    /* Emit */
    // "declaration": true,                              /* Generate .d.ts files from TypeScript and JavaScript files in your project. */
    // "declarationMap": true,                           /* Create sourcemaps for d.ts files. */
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    // "sourceMap": true,                                /* Create source map files for emitted JavaScript files. */
    // "inlineSourceMap": true,                          /* Include sourcemap files inside the emitted JavaScript. */
    // "outFile": "./",                                  /* Specify a file that bundles all outputs into one JavaScript file. If 'declaration' is true, also designates a file that bundles all .d.ts output. */
    // "outDir": "./",                                   /* Specify an output folder for all emitted files. */
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    // "importHelpers": true,                            /* Allow importing helper functions from tslib once per project, instead of including them per-file. */
    // "importsNotUsedAsValues": "remove",               /* Specify emit/checking behavior for imports that are only used for types. */
    // "downlevelIteration": true,                       /* Emit more compliant, but verbose and less performant JavaScript for iteration. */
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    // "noEmitOnError": true,                            /* Disable emitting files if any type checking errors are reported. */
    // "preserveConstEnums": true,                       /* Disable erasing 'const enum' declarations in generated code. */
    // "declarationDir": "./",                           /* Specify the output directory for generated declaration files. */
    // "preserveValueImports": true,                     /* Preserve unused imported values in the JavaScript output that would otherwise be removed. */
    /* Interop Constraints */
    // "isolatedModules": true,                          /* Ensure that each file can be safely transpiled without relying on other imports. */
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    // "preserveSymlinks": true,                         /* Disable resolving symlinks to their realpath. This correlates to the same flag in node. */
    "forceConsistentCasingInFileNames": true, /* Ensure that casing is correct in imports. */
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    "strict": true, /* Enable all strict type-checking options. */
    // "noImplicitAny": true,                            /* Enable error reporting for expressions and declarations with an implied 'any' type. */
    // "strictNullChecks": true,                         /* When type checking, take into account 'null' and 'undefined'. */
    // "strictFunctionTypes": true,                      /* When assigning functions, check to ensure parameters and the return values are subtype-compatible. */
    // "strictBindCallApply": true,                      /* Check that the arguments for 'bind', 'call', and 'apply' methods match the original function. */
    // "strictPropertyInitialization": true,             /* Check for class properties that are declared but not set in the constructor. */
    // "noImplicitThis": true,                           /* Enable error reporting when 'this' is given the type 'any'. */
    // "useUnknownInCatchVariables": true,               /* Default catch clause variables as 'unknown' instead of 'any'. */
    // "alwaysStrict": true,                             /* Ensure 'use strict' is always emitted. */
    // "noUnusedLocals": true,                           /* Enable error reporting when local variables aren't read. */
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    // "exactOptionalPropertyTypes": true,               /* Interpret optional property types as written, rather than adding 'undefined'. */
    // "noImplicitReturns": true,                        /* Enable error reporting for codepaths that do not explicitly return in a function. */
    // "noFallthroughCasesInSwitch": true,               /* Enable error reporting for fallthrough cases in switch statements. */
    // "noUncheckedIndexedAccess": true,                 /* Add 'undefined' to a type when accessed using an index. */
    // "noImplicitOverride": true,                       /* Ensure overriding members in derived classes are marked with an override modifier. */
    // "noPropertyAccessFromIndexSignature": true,       /* Enforces using indexed accessors for keys declared using an indexed type. */
    // "allowUnusedLabels": true,                        /* Disable error reporting for unused labels. */
    // "allowUnreachableCode": true,                     /* Disable error reporting for unreachable code. */
    /* Completeness */
    // "skipDefaultLibCheck": true,                      /* Skip type checking .d.ts files that are included with TypeScript. */
    "skipLibCheck": true /* Skip type checking all .d.ts files. */
  }
}

zod.ts

import { z } from 'zod';
import * as assert from 'node:assert/strict';

/*
Zod schema where an attribute is added to the schema based on value of other attribute.
Consider a schema with 'country' attribute that will have two possible values: 'USA' and 'Canada'
If the country == 'USA', the object should have 'state' attribute and 'province' attribute must not be present.
If the country == 'Canada', the object should have 'province' attribute with allowed values of 'Ontario' or 'ON'
  and 'state' attribute must not be present.
There are some common attributes that should be added to the schema regardless of 'country' value.
*/

const Base = z.object({
  name: z.string(),
});

const CountryEnum = z.enum(['USA', 'Canada']);

const ProvinceEnum = z.enum(['Ontario', 'ON']);

const USState = z.object({
  country: z.literal(CountryEnum.Enum.USA),
  state: z.string().nonempty(),
});

const CanadaProvince = z.object({
  country: z.literal(CountryEnum.Enum.Canada),
  province: ProvinceEnum,
});

const Schema = z.discriminatedUnion('country', [
  Base.merge(USState).strict(),
  Base.merge(CanadaProvince).strict(),
]);

// Just to demonstrate the type. Hover on Person to see the type.
type Person = z.infer<typeof Schema>;

const testUsPersonWithState = () => {
  const person = {
    name: 'Joe',
    country: 'USA',
    state: 'DC',
  };

  assert.ok(Schema.parse(person));
};
testUsPersonWithState();

const testUsPersonWithoutState = () => {
  const person = {
    name: 'Joe',
    country: 'USA',
  };
  const res = Schema.safeParse(person);
  if (!res.success) {
    const err = res.error.issues[0];
    assert.equal(err.message, 'Required');
    assert.equal(err.path[0], 'state');
  }
};
testUsPersonWithoutState();

const testUsPersonWithStateAndProvince = () => {
  const person = {
    name: 'Joe',
    country: 'USA',
    state: 'DC',
    province: 'QC',
  };
  const res = Schema.safeParse(person);
  if (!res.success) {
    const err = res.error.issues[0];
    assert.equal(err.code, 'unrecognized_keys');
    assert.equal(err.keys[0], 'province');
  }
};
testUsPersonWithStateAndProvince();

const testCanadaPersonWithRightProvince = () => {
  const person = {
    name: 'Justin',
    country: 'Canada',
    province: 'ON',
  };
  assert.ok(Schema.parse(person));
};
testCanadaPersonWithRightProvince();

const testCanadaPersonWithRightProvince2 = () => {
  const person = {
    name: 'Justin',
    country: 'Canada',
    province: 'Ontario',
  };
  assert.ok(Schema.parse(person));
};
testCanadaPersonWithRightProvince2();

const testCanadaPersonWithWrongProvince = () => {
  const person = {
    name: 'Justin',
    country: 'Canada',
    province: 'QC',
  };
  const res = Schema.safeParse(person);
  if (!res.success) {
    const err = res.error.issues[0];
    assert.equal(err.code, 'invalid_enum_value');
    assert.equal(err.received, 'QC');
    assert.equal(err.path[0], 'province');
  }
};
testCanadaPersonWithWrongProvince();

const testCanadaPersonWithState = () => {
  const person = {
    name: 'Justin',
    country: 'Canada',
    province: 'ON',
    state: 'ON',
  };
  const res = Schema.safeParse(person);
  if (!res.success) {
    const err = res.error.issues[0];
    assert.equal(err.code, 'unrecognized_keys');
    assert.equal(err.keys[0], 'state');
  }
};
testCanadaPersonWithState();