Sequelize unique slugify function. The model needs to have a slug and title field.

slugify.js

function toSlug(str) {
  return str.replace(/[^\w\s\-]/g, ' ')
    .split(' ')
    .filter(function(substr) {
      return (substr.length > 0);
    })
    .join('-')
  ;
}

function slugify(Model) {
  return function(instance, options, cb) {
    if (instance.title !== undefined) {
      var slug = instance.slug || toSlug( instance.title );
      Model.find({ where: { slug: slug } }).then( function(found) {
        if (found === null) {
          instance.slug = slug;
          cb(null, instance);
        } else {
          var count = 1;
          slug += '-';
          (function recursiveFindUniqueSlug() {
            Model.find({ where: { slug: slug + count } })
                .then( function(found) {
              if (found === null) {
                instance.slug = slug + count;
                cb(null, instance);
              } else {
                count++;
                recursiveFindUniqueSlug();
              }
            });
          })();
        }
      });
    } else {
      // if instance title isn't set then let the validation fail
      cb(null, instance);
    }
  };
}

ex: Blog.hook('beforeValidate', slugify(Blog));