objHasProps.js

var vehicles = {
	car: {
		brand: 'Ferrari'
	}	
};

// This check is obviously OK
if (vehicles.car.brand) {
}

// This throws an error for referencing a property of 'stats' because
// 'stats' is undefined
if (vehicles.car.stats.milesPerGallon) {
}

// This helper function lets you check if an object has a certain 
// set of keys in dot notation without throwing an error
if (objHasProps(vehicles, 'car.stats.milesPerGallon')) {
}

function objHasProps (obj, propsList) {
	var pointer = obj,
	props = propsList.split('.'),
	totalProps = props.length,
	currentKey, 
	i;  

	for (i = 0; i < totalProps; i++) {
		currentKey = props[i];
		if (typeof pointer !== 'object' || !currentKey in pointer) { 
			return false; 
		}
		pointer = pointer[currentKey];
	}
	return true; 
}