efficient implementation of Levenshtein algorithm

 In information theory, linguistics, and computer science, the
 Levenshtein distance is a string metric for measuring the difference
 between two sequences.
 Informally, the Levenshtein distance between two words is the
 minimum number of single-character edits (insertions,
 deletions or substitutions) required to change one word into the other.
 .
 This is pure JavaScript implementation for Node.js.
 .
 Node.js is an event-based server-side JavaScript engine.