TypeScript Lab: Invalid Value Gate

LAB / EXPLORATION

TypeScript Lab: Invalid Value Gate

Planned

LAB 015 — TypeScript Data Modeling
Show valid and invalid values against a TypeScript contract.

LAB TypeScript Lab: Invalid Value Gate Preview coming soon

LAB 015

TypeScript Lab: Invalid Value Gate

Concept

Compiler constraints expose invalid assignments before runtime.

Concept

Compiler constraints expose invalid assignments before runtime.

Objective & Explanation

What the project should make visible and why the concept matters.

Learning Target

Objective

Show valid and invalid values against a TypeScript contract.

Explanation

Compiler constraints expose invalid assignments before runtime.

Project Plan

Structure, technologies, data boundary, and source connection.

Structure

project/
├── package.json
├── tsconfig.json
├── index.html
├── styles.css
└── src/
    └── app.ts

Technologies

TypeScript
HTML
CSS

Data Layer

No persistent data layer. Keep all demonstration values inside the standalone project.

Sandbox Source

src/datastore/types.ts

Build Instructions

Build only the focused behavior, then use the visual layer to inspect it.

Setup

Create the standalone project folder and listed files.

Implement

Implement the smallest version that demonstrates the concept.

Run & Inspect

Change one input and observe the visible output change.

Code & Configuration

Starter configuration plus the focused implementation example.

Focused TypeScript

Implement this behavior first, then alter the input.

type Visibility = "public" | "private" | "local" | "hidden";

function isVisibility(value: string): value is Visibility {
  return ["public", "private", "local", "hidden"].includes(value);
}

Starter Configuration

Keep the project independently buildable.

package.json

{
  "type": "module",
  "scripts": { "build": "tsc" },
  "devDependencies": { "typescript": "^7.0.2" }
}

tsconfig.json

{
  "compilerOptions": {
    "rootDir": "./src",
    "outDir": "./dist",
    "target": "ES2022",
    "module": "ES2022",
    "lib": ["ES2022", "DOM"],
    "strict": true,
    "sourceMap": true
  },
  "include": ["src/**/*.ts"]
}

Expected Visual Result

The output is the proof that the concept is working.

Visible Proof

The browser should visibly demonstrate: show valid and invalid values against a TypeScript contract.

Data: None