format-number-on-input.js

/**
 * Format a number while typing it into an input field.
 *
 * @function formatNumberOnInput
 * @param {!Element} element - The input element to format.
 *
 * @example
 *
 *     formatNumberOnInput(document.getElementById('foo');
 */
function formatNumberOnInput(element) {
	element.addEventListener('keyup', function(e) {
		var number = parseInt(this.value.replace(/\D/g, ''), 10);
		this.value = number.toLocaleString() !== 'NaN' ? number.toLocaleString() : '';
	}, false);
}