Is it OK to reuse variables for different data types in terms of performance and memory usage ?
What happens to old data, is it garbage collected immediately after type casting ?
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Is it OK to reuse variables for different data types in terms of performance and memory usage ?
What happens to old data, is it garbage collected immediately after type casting ?
Full disclosure: I have no knowledge of the internals of any particular JavaScript engines. I’m going from general principles of VMs and interpreters.
Usually, variable names just refer to other memory locations. So, whether you remove an old variable (which happens when it goes out of scope) and introduce a new one, or replace the current contents with a new object, doesn’t matter much in terms of memory allocation.
Garbage collection might be different in each implementation. Immediate garbage collection is difficult; the only way I can think of doing it involves reference counters, and it’s tough to make that work even for cyclic data structures. So, most garbage collectors in the wild do non-immediate collection cycles where, each time, a whole bunch of data gets removed. The cycles might, for example, be run automatically when memory use goes above a certain threshold within the engine (but it’ll usually be more refined than that).