TypeScript Lab: Cache Before and After

LAB / EXPLORATION

TypeScript Lab: Cache Before and After

Planned

LAB 037 — Data Transformation
Compare first database lookup with cached reuse.

LAB TypeScript Lab: Cache Before and After Preview coming soon

LAB 037

TypeScript Lab: Cache Before and After

Concept

A Map can avoid repeating an expensive lookup after the first result.

Concept

A Map can avoid repeating an expensive lookup after the first result.

Objective & Explanation

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

Learning Target

Objective

Compare first database lookup with cached reuse.

Explanation

A Map can avoid repeating an expensive lookup after the first result.

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
JSON

Data Layer

Use a small local object, array, or JSON fixture so the transformation stays visible.

Sandbox Source

src/generator/generate.ts → recordCategoryCache

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.

const cache = new Map<string, string[]>();

function categoriesFor(id: string): string[] {
  const cached = cache.get(id);
  if (cached) return cached;

  const result = lookupCategories(id);
  cache.set(id, result);
  return result;
}

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: compare first database lookup with cached reuse.

Data: JSON