Improving Patterns - Getting rid of Multiple Conditionals

While implementing a function at work, I had a basic and common solution. While reviewing, my coworker (Senior dev) proposed another one, much more elegant.

To recreate the situation, let’s assume we want to determine a parent directory from a path. The input is the path name, the expected output is the parent directory as a formatted string. Let’s assume we have a capitalize function available in our project called ‘capitalizeMyString’.

Given 6 different inputs, expecting their respective outputs:

'sedans/honda-civic'           --> 'Sedans',
'sedans/toyota-corolla'        --> 'Sedans',
'long-sedans/mercedes-class-s' --> 'Sedans',
'trucks/ford-f150'             --> 'Trucks',
'suvs/chevrolet-tahoe'         --> 'Suvs',
'small-suvs/nissan-juke'       --> 'Suvs',

A basic solution might be using multiple conditionals (could be a switch):

function findParentDir(path) {
	const splitPath = path.split('/');
	
	if (splitPath[0] === 'sedans') return 'Sedans';
	if (splitPath[0] === 'long-sedans') return 'Sedans';
	if (splitPath[0] === 'trucks') return 'Trucks';
	if (splitPath[0] === 'suvs') return 'Suvs';
	if (splitPath[0] === 'small-suvs') return 'Suvs'; 
}

A more elegant solution might be:

function findParentDir(path) {
	const splitPath = path.split('/');

	return {
		'long-sedans': 'Sedans',
		'small-suvs': 'Suvs',
	} [splitPath[0]] || capitalizeMyString(splitPath[0]);
}

How To Think About It

There are some questions that might come in handy:

• What does the task/function needs to achieving?
• Why are the conditionals needed? Compare the condition to the part inside the block, and notice the differences/similarities . In this case we match a string and return another and both are very similar.
• How much variety of input to output is there? Some of those inputs are only capitalized.
• Are there “special cases” ? In this case only two (long-sedans and small-suvs).

Conclusion

When doing pattern matching and small transformations/formatting, if the input is very similar to the expected output, and if there are special cases to handle, this makes a very clean solution. It is also faster than having to visit and check every condition when necessary, since we’re using an object. A clumsy console.time() comparison seems to show the second solution is 15 milliseconds faster on the inputs above.