// JavaScript Document

function increment (inputField, action) {
	
	var currentValue = $(inputField).value;
	var newValue = currentValue;
	var delta = 0;
	
	currentValue = currentValue.replace(/[^0-9]/g, '');
	if (currentValue.length > 0) {
		currentValue = parseInt (currentValue);
	} else {
		currentValue = 0;
	}
	
	switch (action) {
		case 'plus':
			delta = 1;
			break;
		case 'minus':
			delta = -1;
			if (currentValue + delta < 0) { 
				delta = -currentValue;
			} 
			break;	
	}
	
	newValue = currentValue + delta;
	$(inputField).value = newValue;
	
	return false; 
}