Was reading http://jspro.com/raw-javascript/intelligent-string-abbreviation/ and decided to try and clean up the example. I then made another version which separated specific functionality into individual functions. Finally I made a third variation which made dependencies external.

1.abbreviate.js

/**
 * Shorten a string by a specified number of characters and end the string 
 * using either a user specified suffix or a default suffix.
 * Ensures string is not abbreviated prematurely (e.g. half way through a word)
 * 
 * @param {string} user specified string
 * @param {number} the maximum allowed characters before abbreviating
 * @param {string} the characters used to end the string
 * @return {string} the abbreviated string
 */
function abbreviate (user_str, user_max, user_suffix) {
    var startend_spaces = /^\s+|\s+$/g;
    var linebreak_spaces = /[\r\n]*\s*[\r\n]+/g;
    var tab_spaces = /[ \t]+/g;
    var ending_space = /[ ]$/g;
    var abbr = '';
    var suffix = (typeof user_suffix !== 'undefined' ? user_suffix : '...');
    var max = user_max - suffix.length;
    var counter = 0;
    var string = user_str;
    var len;

    // if after cleaning up all extraneous white space, if the length of the 
    // string is less than the `max` value then just return the string
    if ((string = string.replace(startend_spaces, '').replace(linebreak_spaces, ' ').replace(tab_spaces, ' ')).length <= max) {
        return string;
    }

    string = string.split(' ');
    len = string.length;

    while (counter < len) {
        // individual characters of a string can be accessed via bracket notation
        if ((abbr + string[counter]).length < max) {
            abbr += string[counter] + ' ';
        } else {
            break;
        }

        counter++;
    }

    return abbr.replace(ending_space, '') + suffix;
}

// Example usage:
console.log(abbreviate('this is my very long string that probably should be cropped at some point soon', 11, '!!!'));
console.log(abbreviate('this is my very long string that probably should be cropped at some point soon', 20));

2.more-functional-version.js

/**
 * Shorten a string by a specified number of characters and end the string 
 * using either a user specified suffix or a default suffix.
 * Ensures string is not abbreviated prematurely (e.g. half way through a word)
 * 
 * @param {string} user specified string
 * @param {number} the maximum allowed characters before abbreviating
 * @param {string} the characters used to end the string
 * @return {string} the abbreviated string
 */
function abbreviate (user_str, user_max, user_suffix) {
    /**
     * Code Structure:
     * - Variables
     * - Functions
     *   - clean_string
     *   - is_too_short
     *   - crop
     * - Initialisation
     */
    var suffix = (typeof user_suffix !== 'undefined' ? user_suffix : '...');
    var max = user_max - suffix.length;
    var string = user_str;

    function clean_string(){
        var startend_spaces = /^\s+|\s+$/g;
        var linebreak_spaces = /[\r\n]*\s*[\r\n]+/g;
        var tab_spaces = /[ \t]+/g;

        string = string.replace(startend_spaces, '').replace(linebreak_spaces, ' ').replace(tab_spaces, ' ');
    }

    function is_too_short(){
        return string.length <= max;
    }

    function crop(){
        var abbr = '';
        var counter = 0;
        var len;
        var ending_space = /[ ]$/g;

        string = string.split(' ');
        len = string.length;

        while (counter < len) {
            // individual characters of a string can be accessed via bracket notation
            if ((abbr + string[counter]).length < max) {
                abbr += string[counter] + ' ';
            } else {
                break;
            }

            counter++;
        }

        return abbr.replace(ending_space, '') + suffix;
    }

    clean_string(); // remove all extraneous white space

    if (is_too_short()) {
        return string;
    }

    return crop();
}

// Example usage:
console.log(abbreviate('this is my very long string that probably should be cropped at some point soon', 11, '!!!'));
console.log(abbreviate('this is my very long string that probably should be cropped at some point soon', 20));

3.evenmore-functional.js

/**
 * Shorten a string by a specified number of characters and end the string 
 * using either a user specified suffix or a default suffix.
 * Ensures string is not abbreviated prematurely (e.g. half way through a word)
 * 
 * Dependencies:
 *     - clean_string
 *     - is_too_short
 *     - crop
 * 
 * @param user_str {string} user specified string
 * @param user_max {number} the maximum allowed characters before abbreviating
 * @param user_suffix {string} the characters used to end the string
 * @return {string} the abbreviated string
 */
function abbreviate (user_str, user_max, user_suffix) {
    var suffix = (typeof user_suffix !== 'undefined' ? user_suffix : '...');
    var max = user_max - suffix.length;
    var string = clean_string(user_str); // remove all extraneous white space

    if (shorter_than(string, max)) {
        return string;
    }

    return crop(string, max, suffix);
}

/**
 * Removes any unnecessary spaces from the specified string
 * 
 * @param string {string} user specified string
 * @return {string} the string cleared of unnecessary spaces
 */
function clean_string (string) {
    var startend_spaces = /^\s+|\s+$/g;
    var linebreak_spaces = /[\r\n]*\s*[\r\n]+/g;
    var tab_spaces = /[ \t]+/g;

    return string.replace(startend_spaces, '').replace(linebreak_spaces, ' ').replace(tab_spaces, ' ');
}

/**
 * Checks if the string length is less or equal to the maximum allowed
 * 
 * @param string {string} user specified string
 * @param max {number} the maximum allowed characters before abbreviating
 * @return {boolean} whether the length of the string exceeds the maximum
 */
function shorter_than (string, max) {
    return string.length <= max;
}

/**
 * Crops the string so its length is under the max allowed, and also
 * adds the specified suffix to the end of the string
 * Ensures string is not abbreviated prematurely (e.g. half way through a word)
 * 
 * @param string {string} user specified string
 * @param max {number} the maximum allowed characters before abbreviating
 * @param suffix {string} the characters used to end the string
 * @return {string} the abbreviated string
 */
function crop (string, max, suffix) {
    var abbr = '';
    var counter = 0;
    var len;
    var ending_space = /[ ]$/g;

    string = string.split(' ');
    len = string.length;

    while (counter < len) {
        // individual characters of a string can be accessed via bracket notation
        if ((abbr + string[counter]).length < max) {
            abbr += string[counter] + ' ';
        } else {
            break;
        }

        counter++;
    }

    return abbr.replace(ending_space, '') + suffix;
}

// Example usage:
console.log(abbreviate('this is my very long string that probably should be cropped at some point soon', 11, '!!!'));
console.log(abbreviate('this is my very long string that probably should be cropped at some point soon', 20));