format number to add thousand separator (e.g. `,`) in js -- inspired by http://www.mredkj.com/javascript/nfbasic.html

format.js

function format(num, fmt) {
    if (isNaN(Number(num))) {
        throw new TypeError('Not a number');
    }
    if (typeof fmt.scale == 'number') {
        num = Number(num).toFixed(fmt.scale);
    }
    num = String(num).replace('.', fmt.outDecSep||'.');
    var regexp = /(\d+)(\d{3})/;
    while(regexp.test(num)) {
        num = num.replace(regexp, ['$1', '$2'].join(fmt.thousandSep||','));
    }
    return num;
}

regexp_format.js

function format(input, scale) {
    if (isNaN(Number(input))) {
        throw new TypeError('not a number');
    }
    var num = String(Number(input).toFixed(scale)),
        regexp = /(\d+)(\d{3})/;
    while (regexp.test(num)) {
        num = num.replace(regexp, ['$1', '$2'].join(','));
    }
    return num;
}

str_format.js

function format(input, scale) {
    var chars = String(Number(input).toFixed(scale)).split('').reverse(),
        dot = chars.indexOf('.'),
        integral = chars.slice(dot + 1),
        decimal = dot > -1 ? chars.slice(0, dot) : [],
        after = [];
    integral.forEach(function (c, i) {
        if (i > 0 && i%3 == 0) {
            after.push(',')
        }
        after.push(c)
    });
    decimal.length && Array.prototype.unshift.apply(after, decimal.concat('.'));
    return after.reverse().join('');
}

format('1234.567', {scale: 2, outDecSep: ',', thousandSep: '.'}) // => 1.234,57