I stole this https://gist.github.com/codeguy/6684588?permalink_comment_id=3243980#gistcomment-3243980

slugify.js

function slugify(text) {
  // from https://gist.github.com/codeguy/6684588?permalink_comment_id=3243980#gistcomment-3243980
  return text
    .toString()                           // Cast to string (optional)
    .normalize('NFKD')            // The normalize() using NFKD method returns the Unicode Normalization Form of a given string.
    .toLowerCase()                  // Convert the string to lowercase letters
    .trim()                         // Remove whitespace from both sides of a string (optional)
    .replace(/\s+/g, '-')            // Replace spaces with -
        .replace(/[^\w\-]+/g, '')			// Remove all non-word chars
    .replace(/\-\-+/g, '-')        	// Replace multiple - with single -
    .replace(/\-$/g, '');						// Remove trailing -
}

In my implementation I ended up with a trailing dash slugify('Jurassic Park III, 2001 - ★★★') so I added the final replace.