idf.js

function inverseDocumentFrequency(document){
    // calculates the inverse document frequency of every sentence
    const words_without_stopwords = prettify(document);
    const unique_words_set = uniqueWords(words_without_stopwords);

    const sentences = document.split(".").map(item => item.trim());
    sentences[0] = sentences[0].substring(146);

    const lengthOfDocuments = sentences.length;
    // prettifys each sentence so it doesn't have stopwords

    const wordCountAll = countWords(words_without_stopwords);

    // counts words of each sentence
    // as each sentence is a document
    wordCountSentences = [];
    for (let i = 0; i <= lengthOfDocuments - 1; i ++){
        wordCountSentences.push(countWords(prettify(sentences[i])));
    }

    // calculate TF values of all documents
    let IDFVals = {};