Reading and parsing unstructured files with JavaScript

It's marvelous to have input files where the information is well formed, that is, the number of columns and the type of its data is precise, all rows follow the same pattern, and so on. However, it is common to find input files where the information has little or no structure, or the structure doesn't follow the matrix (n rows by m columns) you expect. This is one of the situations where JavaScript comes to the rescue.