This is an uninitialized object members of the error, the specific location for the C * Element (here for CLiElement) at offset 0x10, this pointer to a structure, the structure of the offset 0 is a point to itself (?) The object pointer , offset for the 4 point to the parent DOM element.When you call document.createElement ( "html"), the code does not initialize the members, resulting in a null pointer reference error. As the DOM element is the _MemAllocClear through mshtml to allocate memory function, the function of memory allocation will be cleared, can not take advantage of this mistake