created based off of an archived jsperf benchmark: http://web.archive.org/web/20191008221700/https://jsperf.com/foreach-vs-for-loop-vs-for-in-vs-for-of-vs-babel-for-of change var to let. for of returns the value directly. So you don't get value from testData array.

performance comparison of ways to find if an array contains a value

Comparing the performance of different implementations of 2-Tuple cache (mapping a pair of numbers to another number) when being used to achieve memoization a recursive algorithm.