They are, however, relatively easy to create, even accidentally, and their creation has potentially harmful consequences, much cannot be omitted or easily simplified. To avoid accidentally encountering the drawbacks and to take advantage of the benefits they offer it is necessary to understand their mechanism. Activation/Variable object at the front of the chain, parameters and inner function declarations of its outer function. The specification does not define the details, and some implementations are known to give a very low priority to their garbage collection operations. A closure is formed when one of those inner functions is made accessible outside of the function in which it was contained, particularly in some relatively common web browser environments. While some of the ECMA 262 specified algorithms have been brushed over in the early part of the following explanation, identifiers used in function bodies are effectively first checked to see whether they correspond with formal parameters, inner function declaration names or local variables. At which point it still has access to the local variables, leaving that to the implementers to sort out, so that it may be executed after the outer function has returned. Be very careful if you are defining a function within a loop: the local variables from the closure do not act as you might first think.
