What is weak reference? What are the weak reference data types in ES6? What are weak references in JS?

Weak reference ：

WeakSet The objects in are all weak references , Garbage collection mechanism does not consider WeakSet Reference to the object , in other words , If no other object references that object , Then the garbage collection mechanism will automatically reclaim the memory occupied by the object , Regardless of whether the object still exists in WeakSet In .

This is because the garbage collection mechanism depends on the reachability of objects （reachability） To determine recycling , If the object can still be accessed , The garbage collection mechanism will not free this memory . After you finish using this value , Sometimes I forget to dereference , Causes memory not to be released , This can lead to memory leaks .WeakSet The quotation in it , Not included in the garbage collection mechanism , So there is no such problem . therefore ,WeakSet Suitable for temporary storage of a group of objects , And storing information bound to objects . As long as these objects disappear outside , It's in WeakSet The references in it will disappear automatically .

Because of the above characteristics ,WeakSet Members of are not suitable for reference , Because it will disappear at any time . in addition , because WeakSet How many members are there inside , Depends on whether the garbage collection mechanism is running , It is likely that the number of members before and after running is different , And when the garbage collection mechanism will run is unpredictable , therefore ES6 Regulations WeakSet Non traversal . And of course not size attribute , Because the amount of data is also uncertain .

These features also apply to WeakMap structure