Naive helper functions...

dateFormatter.js

var d = new Date();


function formatDate(dt, format, glue) {
    glue        = glue  || '/';
    format      = format || 'mm/dd/yyyy';

    if (typeof dt === 'string') {
        dt = new Date(dt);
    }

    let parts   = format.match(/(\w+)/gi);
    let res     = '';

    parts = parts.map((str) => {

        let res = '';

        let flag = str[0].toLowerCase();

        // process day
        if (flag === 'd') {
            res = '' + dt.getDate();
        }

        // process day
        if (flag === 'm') {
            res = '' + (dt.getMonth() + 1);
        }

        // apply leading zeroes to result
        if (str.length > 1 && res.length < 2) {
            res = '0' + res;
        }

        // process year
        if (flag === 'y') {
            res = '' + dt.getFullYear().toString();

            if (str.length <= 2) {
                res = res.substr(-2);
            }
        }

        return res;
    });

    parts = parts.join(glue);

    console.log(format, parts);
}


formatDate(d, 'mm/dd/yyyy');
formatDate(d, 'mm/dd/yyy');
formatDate(d, 'mm/dd/yy');
formatDate(d, 'dd/mm/yy');
formatDate(d, 'mm/yy', '-');

phoneFormatter.js

// /**
//  * Naive phone number formatter based on US phone numbers
//  * @param  {string} num         Phone number to be parsed and formatted
//  * @param  {object} opts        String of target opts to format phone number with
//  *         {string} - locale
//  * @param  {bool}   opts        False to return the stripped phone number
//  * @return {string}             The formatted phone number as string
//  */
// function formatPhone(num, opts) {

//     // clean up the phone number string so we only have integers to work with
//     num = num
//         .trim()
//         .replace(/[^\d]+/g, '')
//         ;

//     // return the stripped value if options are turned off
//     if (opts === false) {
//         return num;
//     }

//     // define formats
//     defaults = {
//         locale:         'en-us',
//         stripExt:       false,
//         stripPrefix:    false,
//     };

//     let formatters = {
//         'en-us': formatUS,
//     };

//     //
//     opts = Object.assign({}, defaults, opts);

//     return formatters[opts.locale](opts);
// }



// function formatUS(num, opts) {

//     // bug out if this is unlikely to be a real phone number
//     if (num.length < 7 || (7 < num.length && num.length < 10)) {
//         return false;
//     }

//     // split out the different parts of the phone number
//     num = num.match(/(1)?(\d{3})?(\d{3})(\d{4})(\d+)?/);

//     let res = '';

//     let prefix      = num[1];
//     let areacode    = num[2];
//     let suffix      = num[3];
//     let postfix     = num[4];
//     let ext         = num[5];

//     res += prefix ? '+1 ' : '';
//     res += areacode ? `(${areacode}) ` : '';
//     res += `${suffix}-${postfix}`;
//     res += ext ? ` +${ext}` : '';

// }


/**
 * Naive phone number formatter based on US phone numbers
 * @param  {string} num         Phone number to be parsed and formatted
 * @param  {object} opts        String of target opts to format phone number with
 *         {string} - locale
 * @param  {bool}   opts        False to return the stripped phone number
 * @return {string}             The formatted phone number as string
 */
function formatPhone(num, opts) {

    // clean up the phone number string so we only have integers to work with
    var num = num
        .trim()
        .replace(/[^\d]+/g, '')
        ;

    // return the stripped value if options are turned off
    if (opts === false) {
        return num;
    }

    // define formats
    defaults = {
        // locale:         'en-us',
        stripExt:       false,
        stripPrefix:    false,
    };

    // map overrides accordingly
    opts = Object.assign({}, defaults, opts);

    // bug out if this is unlikely to be a real phone number
    if (num.length < 7 || (7 < num.length && num.length < 10)) {
        return false;
    }

    // split out the different parts of the phone number
    num = num.match(/(1)?(\d{3})?(\d{3})(\d{4})(\d+)?/);

    var prefix      = num[1] && !opts.stripPrefix ? '+1 '             : '';
    var areacode    = num[2]                      ? `(${num[2]}) `    : '';
    var core        = `${num[3]}-${num[4]}`;
    var ext         = num[5] && !opts.stripExt    ? ` +${num[5]}`     : '';

    // compose US phone number
    return [ prefix, areacode, core, ext ].join('');
}




var num;

num = '       5551234567       '; console.log(num, 'becomes', formatPhone(num));
num = '     555.123.4567       '; console.log(num, 'becomes', formatPhone(num));
num = '   (555) 123-4567       '; console.log(num, 'becomes', formatPhone(num));
num = '   (555) 123 4567       '; console.log(num, 'becomes', formatPhone(num));
num = '   (555) 123 4567 +1050 '; console.log(num, 'becomes', formatPhone(num));
num = '+1 (555) 123 4567 +1050 '; console.log(num, 'becomes', formatPhone(num));
num = '            12567       '; console.log(num, 'becomes', formatPhone(num));
num = '        123-45675       '; console.log(num, 'becomes', formatPhone(num));
num = '     555-123-4567       '; console.log(num, 'becomes', formatPhone(num));
num = '    1555-123-4567       '; console.log(num, 'becomes', formatPhone(num));
num = '      15551234567       '; console.log(num, 'becomes', formatPhone(num));
num = '      15551234567+12346 '; console.log(num, 'becomes', formatPhone(num));
num = '     +15551234567       '; console.log(num, 'becomes', formatPhone(num));