JavaScript Word Frequency + Some Options

js_word_frequency.js

/**
 * Find how often words appear in a string, optionally
 * limiting to ones that occur with a given frequency.
 *
 * @param {String}      searchString        The sentence to search on.
 * @param {Integer}     frequency           The frequency at which you want to find words with.
 * @param {Boolean}     caseSensitive       Whether to use case sensitive searching.
 * @param {Booolean}    stripPunctuation    If punctuation should be removed before parsing.
 */
var wordFrequency = function( searchString, frequency, caseSensitive, stripPunctuation ) {
    
    searchString = ( caseSensitive ? searchString : searchString.toLowerCase() );
    searchString = ( stripPunctuation ? searchString.replace(/[\.,-\/#!$%\^&\*;:{}=\-_`~()]/g, '') : searchString );
    
    var found = {},
        words = searchString.split(' ');
    
    words.map( function( word ) {
        if ( word.length >= 1 ) {
            if ( found[word] ) {
                found[word]++;
            }
            else {
                found[word] = 1;
            }
        }
    });
    
    if ( frequency ) {
        for ( var word in found ) {
            if ( found[word] != frequency ) {
                delete found[word];
            }
        }
    }
    
    return found;
    
};

// Find words that appear exactly 2 times
var result = wordFrequency( 'The king is dead, long live the king', 2, false );

for ( var word in result ) {
    console.log( word );
}

// Find the frequency of all words
var result = wordFrequency( 'The king, is dead, long live the king', false, false, true );

for ( var word in result ) {
    console.log( word + ': ' + result[word] );
}