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Tewolde Luwam

Tewolde Luwam

3 years ago

Typed Data Generator for Deno

Typed Data Generator (TDG) for Deno

This library assumes that structured data such as JSON, CSV, etc. are kept as TypeScript *.ts source files and then use this typed-data-gen library to generate their final formats.

The primary benefit is that no special JSON Schema or other schema management is necessary, all data structures are defined in TypeScript. By sticking with TypeScript, Visual Studio Code and other TypeScript-based editors can provide excellent syntax highlighting and error detection support.

You can create either *.ts files that generate *.json files or, you can use existing *.json files with companion *.ts schema files that can validate any existing JSON files with any structure that TypeScript natively supports.

Usage - TypeScript that generates JSON

To use this library to generate valid, type-safe JSON, first create any TypeScript file and define any arbitrary data structures. Inside the TypeScript file, the content or any other variable can be generated organically or automatically with any level of complexity. Then, just add CliArgsEmitterat the bottom of the file.

import * as typedDataGen from "https://denopkg.com/shah/tsd-typed-data-gen/mod.ts";

export interface HomePage {
  hero: HeroContent[];
  sections: Section[];
  whyMedigyTitle: string;
  whyMedigyDescription: string;
  whyMedigyButton: string;
}

const content: HomePage = {
  hero: [...],
  sections: [...],
  whyMedigyTitle: someFunctionResult(...),
  whyMedigyDescription:  // multi-line templates are OK too
    `Medigy is crowd-sourced and peer network-based. Buyers 
     get access to rich content about the digital health products 
     they’re looking for. Influencers have a new place to build and
     engage with a community around their areas of expertise.`,
  whyMedigyButton: "Why Medigy?",
};

if (import.meta.main) {
  new typedDataGen.CliArgsEmitter(import.meta.url).emitJSON(content);
}

Assuming the file is called my-data.ts then you can do the following to emit the typed data as JSON to STDOUT:

deno run -A my-data.ts

It’s even more powerful when the source data is at another location:

deno run -A https://raw.githubusercontent.com/shah/tsd-typed-data-gen/master/test-data.tdg.ts local-file.auto.json

Or, you can have it default it to a regular file with the same name at the same location if it’s on the local file system (note that there’s a space between the my-data.ts and .json CLI argument):

deno run -A my-data.ts .json

The above will create my-data.auto.json to indicate that it’s automatically generated JSON and shouldn’t be edited directly.

Or, you can have it default it to a regular file with a different name:

deno run -A my-data.ts another-name.json

Usage - JSON that can use TypeScript to verify its schema

Sometimes the source JSON cannot be modified but we want to verify that JSON content matches a TypeScript Schema. The TDG library allows for what we call a “JSON Module”.

Assume we want to verify that a JSON file matches the following interface, in a file called json-module.test-schema.ts:

export interface Expected {
  readonly text: string;
  readonly numeric: number;
}

Here’s how we can easily validate it:

const validJsonModule = new JsonModule(
  {
    imports: [
      {
        denoCompilerSrcKey: "/json-module.test-schema.ts",
        typeScriptImportRef:
          `import type * as mod from "./json-module.test-schema.ts"`,
        importedRefSourceCode: new mod.TextFileSourceCode(
          "./json-module.test-schema.ts",
        ),
      },
    ],
    moduleName: "invalid.auto.ts",
    jsonContentFileName: "invalid.json",
    primaryConstName: "expected",
    primaryConstTsType: "mod.Expected",
  },
);

const tsSrcDiagnostics = await validJsonModule.validate();
if(tsSrcDiagnostics) {
  // if validate returns diagnostics it means the JSON file does not
  // match our expected interface. 
  console.log(Deno.formatDiagnostics(tsSrcDiagnostics));
}

If you ran the above code on JSON that looks like this, in a file called invalid.json:

{
  "text": "text value",
  "numeric": "bad number"
}

You would see this error:

 TS2322 [ERROR]: Type 'string' is not assignable to type 'number'.
  numeric: 'bad number'
  ~~~~~~~
    at /test-invalid.ts:6:3

    The expected type comes from property 'numeric' which is declared here on type 'Expected'
      readonly numeric: number;
               ~~~~~~~
        at /json-module.test-schema.ts:3:12

The way the error is generated is that the TDG JSON Module library simply creates a dynamic TypeScript file, compiles it, and shows the resulting errors. Here’s what the interim *.ts file looks like:

import type * as mod from "./json-module.test-schema.ts";

export const expected: mod.Expected = {
  text: 'text value',
  numeric: 'bad number'
};

export default expected;

The JSON Modules feature allows you to use the full power of TypeScript to validate a JSON file against a verifiable structure instead of having to rely on less reliable strategies such as JSON Schema.

Download Details:

Author: shah

Source Code: https://github.com/shah/tsd-typed-data-gen

#deno #nodejs #node #javascript

Typed Data Generator for Deno
4.10 GEEK