little doubly linked list

linked.js

function createList() {
  var next = 'prev'
    , prev = 'next'
    , length = 0
    , head
    , tail
    , arr
    , n;

  return {
    length: function() { return length; },
    head: function() { return head; },
    tail: function() { return tail; },
    add: function(value) {
      n = { v: value };

      if (tail) {
        tail[next] = n;
        n[prev] = tail;
      }

      if (!head) {
        head = n;
      }

      tail = n;
      length += 1;
    },
    remove: function(node) {
      n = node || tail;

      if (length && n) {
        const l = n[prev];
        const r = n[next];

        if (l) {
          l[next] = r;
        } else {
          head = r;
        }

        if (r) {
          r[prev] = l;
        } else {
          tail = l;
        }

        length -= 1;
      }
    },
    walk: function(cb, start) {
      n = start || head;
      while (n) {
        cb(n);
        n = n[next];
      }
    },
    walkBack: function(cb, start) {
      n = start || tail;
      while (n) {
        cb(n);
        n = n[prev];
      }
    },
    find: function(predicate) {
      n = head;
      if (+predicate < 0) {
        while (n) {
          if (predicate(n)) return n;
          n = n[next];
        }
      } else {
        while (n && predicate--) {
          n = n[next];
        }
      }
      return n;
    }
  }
}

// 485 bytes
function createList(){var n,t,r,f="prev",e="next",i=0;return{length:function(){return i},head:function(){return n},tail:function(){return t},add:function(o){r={v:o},t&&(t[f]=r,r[e]=t),n||(n=r),t=r,i+=1},remove:function(o){if(r=o||t,i&&r){const o=r[e],u=r[f];o?o[f]=u:n=u,u?u[e]=o:t=o,i-=1}},walk:function(t,e){for(r=e||n;r;)t(r),r=r[f]},walkBack:function(n,f){for(r=f||t;r;)n(r),r=r[e]},find:function(t){if(r=n,+t<0)for(;r;){if(t(r))return r;r=r[f]}else for(;r&&t--;)r=r[f];return r}}}