Slugify

A slug is the URL-safe version of a title — lowercase, hyphen-separated, and reduced to just letters, digits, and single hyphens (the my-post-title you see in a blog URL or a docs anchor). Write slugify(str) that turns any string into one: "Hello, World!" becomes "hello-world" and "Café Crème" becomes "cafe-creme". The work is in the messy inputs — accented letters, punctuation, and stray or repeated spaces — each of which needs its own cleanup step.

Signature

slugify(str)
// str: any string — a title, heading, or filename
// returns: a slug containing only [a-z0-9-], with no
//   leading, trailing, or doubled hyphens

Examples

slugify('Hello, World!');         // 'hello-world'
slugify('  Multiple   Spaces  '); // 'multiple-spaces'
slugify('Node.js & React');       // 'node-js-react'
slugify('Top 10 Tips');           // 'top-10-tips'

slugify('Café Crème');   // 'cafe-creme'   (accents stripped)
slugify('Crème Brûlée'); // 'creme-brulee'
slugify('!!! ??? ...');  // ''             (all symbols → empty)
slugify('');             // ''

Notes

• Lowercase only. The output uses a–z, 0–9, and -. No uppercase, no spaces, no punctuation.
• Accents become their base letter. é becomes e and ü becomes u, so "Zürich" slugs to "zurich". That means normalizing Unicode, not a hand-written lookup table.
• Collapse, do not multiply. A whole run of non-alphanumeric characters (spaces, punctuation, symbols) becomes a single hyphen — "a & b" is "a-b", never "a---b".
• No hyphens on the ends. Trim any leading or trailing hyphens, so "--Hello--" is "hello".
• Digits stay. Numbers are alphanumeric and survive: "Top 10" keeps its 10.
• Empty is a valid answer. A string with no letters or digits (all spaces or symbols) slugs to "".