js-01-slugify

# Slugify a title

Implement an ES module **`solution.js`** exporting a single function:

```js
export function slugify(input) { /* ... */ }
```

Convert a human title string into a URL slug:

- Lowercase the whole string.
- Treat **any character that is not an ASCII letter (`a–z`) or digit (`0–9`) as a separator** —
  this includes spaces, punctuation, underscores, and non-ASCII letters.
- Replace each **run** of one or more separators with a **single** hyphen (`-`).
- Strip any leading or trailing hyphens from the result.

Return the resulting slug (a string). An input made entirely of separators returns `""`.

Examples:
```js
slugify("Hello World")          // => "hello-world"
slugify("  Hello,  World!  ")   // => "hello-world"
slugify("already-clean")        // => "already-clean"
slugify("Top 10 Tips")          // => "top-10-tips"
slugify("a---b__c")             // => "a-b-c"
slugify("@#$%")                 // => ""
```

import { test } from "node:test";
import { strict as assert } from "node:assert";
import { slugify } from "./solution.js";

test("spaces become single hyphens", () => {
  assert.equal(slugify("Hello World"), "hello-world");
});

test("punctuation collapses and ends are trimmed", () => {
  assert.equal(slugify("  Hello,  World!  "), "hello-world");
});

test("already-clean input is unchanged", () => {
  assert.equal(slugify("already-clean"), "already-clean");
});

test("digits are preserved", () => {
  assert.equal(slugify("Top 10 Tips"), "top-10-tips");
});

test("runs of mixed separators collapse to one hyphen", () => {
  assert.equal(slugify("a---b__c"), "a-b-c");
});

test("leading and trailing junk is trimmed", () => {
  assert.equal(slugify("--Foo Bar--"), "foo-bar");
});

test("all-separator input becomes empty string", () => {
  assert.equal(slugify("@#$%"), "");
});

test("empty string stays empty", () => {
  assert.equal(slugify(""), "");
});

test("non-ASCII letters act as separators", () => {
  assert.equal(slugify("café crème"), "caf-cr-me");
});

You are an expert programmer. Solve the task exactly as specified. Output your solution as fenced code blocks using the required file name(s) and the exact function/type signatures requested. Prefer correctness; do not include prose outside code unless asked.

```js
export function slugify(input) {
  // Lowercase the whole string
  const lower = input.toLowerCase();
  
  // Replace non-alphanumeric characters with a hyphen
  // This handles spaces, punctuation, underscores, and non-ASCII letters
  const replaced = lower.replace(/[^a-z0-9]/g, '-');
  
  // Replace runs of separators with a single hyphen
  const collapsed = replaced.replace(/-+/g, '-');
  
  // Strip leading and trailing hyphens
  return collapsed.replace(/^-+|-+$/g, '');
}
```