* A JS VM can be modeled as a [MicroTask] queue, [MacroTask] queue, and [EventTask] set.
*
* - [MicroTask] queue represents a set of tasks which are executing right after the current stack
* frame becomes clean and before a VM yield. All [MicroTask]s execute in order of insertion
* before VM yield and the next [MacroTask] is executed.
* - [MacroTask] queue represents a set of tasks which are executed one at a time after each VM
* yield. The queue is order by time, and insertions can happen in any location.
* - [EventTask] is a set of tasks which can at any time be inserted to the end of the [MacroTask]
* queue. This happens when the event fires.Zonejs的源码中有这样的注释，想知道 VM yield 是什么意思