Andrew Leedham

Thoughts on simplifying long if statements

webjavascript

I ran into a problem recently where an if statement was getting out of hand. It was quickly becoming unreadable. So I did some thinking on how I could simplify it. The if statement in question was needed to check if 1 of 3 given objects was truthy but only 1. The astute may recognise this as an exclusive or (xor) statement. So let's look at the problem, written out it would have looked something like this:

if (
(term1 && !term2 && !term3) ||
(!term1 && term2 && !term3) ||
(!term1 && !term2 && term3)
) {
// do something
}

Prettier admittedly does a great job of formatting this, but tracking each of the nots (!) are in the correct place is error-prone. So what can we do to improve this? There are several techniques that could be useful here, each with different pros and cons, and each can be useful on there own.

Splitting the if statment into 3 variables

const onlyTerm1 = term1 && !term2 && !term3;
const onlyTerm2 = !term1 && term2 && !term3;
const onlyTerm3 = !term1 && !term2 && term3;
if (onlyTerm1 || onlyTerm2 || onlyTerm3) {
// do something
}

Pros

Cons

Abstracting the logic into a function

function onlyTerm(term, otherTerm1, otherTerm2) {
return term && !otherTerm1 && !otherTerm2;
}

const onlyTerm1 = onlyTerm(term1, term2, term3);
const onlyTerm1 = onlyTerm(term2, term3, term1);
const onlyTerm1 = onlyTerm(term3, term1, term2);
if (onlyTerm1 || onlyTerm2 || onlyTerm3) {
// do something
}

Pros

Cons

Using JavaScripts functional program style Array functions

if ([term1, term2, term3].filter((term) => Boolean(term)).length === 1) {
// do something
}

Pros

Cons

Creating an exclusive or (xor) helper function

function xor(...terms) {
return terms.filter((term) => Boolean(term)).length === 1;
}
if (xor(term1, term2, term3)) {
// do something
}

Pros

Note that yes, with large data sets the xor function is not the most efficient implementation. There is room for optimisation. But on three terms, or likely any number of terms you are likely to put in an if statement, the difference would be negligible. Readability reigns king over micro optimisations in most cases.

Conclusion

Abstracting to functions and variables are two very crucial tools in our programming toolbelts. Each of these techniques can be used in different scenarios. None of them are perfect. But taking the time to think about readability is key not only in shared code-bases, but for yourself when coming back to your code years, months or even weeks later.