TypeScript Lab: SQL Placeholder Factory

LAB / EXPLORATION

TypeScript Lab: SQL Placeholder Factory

Planned

LAB 109 — Validation & Safety
Generate the correct number of SQL parameter placeholders.

LAB TypeScript Lab: SQL Placeholder Factory Preview coming soon

LAB 109

TypeScript Lab: SQL Placeholder Factory

Concept

Dynamic placeholder strings support variable-size prepared IN clauses.

Concept

Dynamic placeholder strings support variable-size prepared IN clauses.

Objective & Explanation

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

Learning Target

Objective

Generate the correct number of SQL parameter placeholders.

Explanation

Dynamic placeholder strings support variable-size prepared IN clauses.

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/local-editor/server.ts → placeholders()

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.

function placeholders(count: number): string {
  return Array.from({ length: count }, () => "?").join(", ");
}

placeholders(4); // ?, ?, ?, ?

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: generate the correct number of SQL parameter placeholders.

Data: None