More morning mind food (at least where I am)...
The new operator allocates memory for objects. How is this memory
deallocated?
If you have ever programmed in C++, you might wonder why JavaScript does not
have a delete operator to match the new operator. The reason for this is
simple: It's not necessary!
In JavaScript, memory for objects is automatically reclaimed whenever there
is no longer need for the object. The JavaScript interpreter tracks
references to objects and deletes them when variables no longer refer to
them.
For example, consider the following JavaScript code:
d = new Array (50);
d = null;
The first statement allocates memory for an Array object large enough to
hold 50 elements, and then records the fact that the new object is
referenced by a variable named d.
The next statement, however, changes d so that instead of referring to the
Array object, it instead contains the special value null. Since there is no
longer any way to access the Array object, the JavaScript interpreter
destroys it by reclaiming the memory that was allocated to it.
Reclaiming memory allocated for objects which can no longer be accessed is
called garbage collection. Allocated objects which are no longer accessible
by variables are called orphan objects.
This next example shows how to modify the above code to prevent the
destruction of the Array object:
d = new Array (50);
e = d; // make e refer to the same object as d
d = null; // disassociate d from the Array object
Since the Array object is referenced by e at the moment it is abandoned by
d, the Array object remains intact.
In conclusion, there is no need to worry about destroying objects in
JavaScript. Garbage collection is performed automatically by the interpreter
whenever objects are no longer useful or documents are unloaded. If you want
to explicitly destroy an object, you can do so by abandoning it -- that is,
by making sure there are no variables that refer to it. (Setting the
variables to null works pretty well for this.)
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