code: function hashUnique(a) {
    var table={},i=0,j=0,l=a.length,x;
    for (;i<l;i++) {
      x=a[i];
      if (table.hasOwnProperty(x)) continue;
      table[x]=1;
      a[j++]=x;
    }
    a.length=j;
    return a;
  }
docs: Unique by toString.
  This function will corrupt the original array but preserve the original order.