constructor() {
        /**
         * Total number of chunks
         */
        this.chunkCount = 0;
        this.chunkOccurrences = new Map();
        this.documents = new Map();
    }
Implementation of tf-idf (term frequency-inverse document frequency) for a set of
documents where each document contains one or more chunks of text.
Each document is identified by a key, and the score for each document is computed
by taking the max score over all the chunks in the document.