Memoizing exercise

Some simple exercises in building a generalized memoizing function.

Each memoizing function improves on the previous as described below.

See test.js for quick testing of the memoizing functions. The console should output 'computed' when the memoized function is called with whichever argument(s) for the first time.

memoizeSingleArgument

• Uses an Object for the cache. Memoized function can only accept a single argument with a primitive or Symbol type.

memoizeSingleArgumentMap

• Improves on the previous memoizing by using a Map for the cache, allowing the memoized function to accept arguments of any type.

memoizeMultipleArgumentsMap

• Improves on the previous memoizing function by structuring the cache as a hash tree, allowing for an arbitrary (and variable) number of arguments to by accepted by the memoized function.
• Has a bug when the memoized function has an argument with value of the string 'value', due to how the leaf node of the tree is designated.

memoizeMultipleArgumentsMapSymbol

• Improves on the previous memoizing function by using a Symbol for the leaf node designation. The string 'value' can now by used as an argument to the memoized function.