Algebraic refactoring - case study

Probably most of you remember algebra exercises from math class, where calculations were done with letters, not numbers. Finally, once we had the simplified form, numbers were substituted for the letters to get the result.

The same method can be used when refactoring the code. This is of course independent of the programming language.

In this case study, I will use what I found during the code review.

The initial code snippet looked like this.

if (!authToken) {
  setInvalidToken(true);
  throw {
    authToken,
    value,
  };
}
if (!value) {
  throw {
    authToken,
    value,
  };
}

if (authToken && value) {
  Cookies.set(`${value}-authToken`, authToken, {
    expires: 1,
  });
  setCustomerInfo(authToken);
} else {
  setInvalidToken(true);
  throw {
    authToken,
    value,
  };
}

It doesn’t matter what the code does. The important thing is that it consists of several repetitive parts.

I will replace some code fragments with letters.

a => authToken
b => value
x => setInvalidToken(true);
y => throw {...}
z => Cookies.set(...) + setCustomerInfo(authToken)

Now, using letters, I will present the same code.

if (!a) { x; y; }
if (!b) { y; }
if (a && b) { z; } else { x; y; }

In the above form, this code is definitely easier to refactor. This can be refactored to the following form:

if (a && b) {
  z;
} else {
  if (a) { x; }
  y;
}

Now we can substitute real values for the letters.

Finally we get:

if (authToken && value) {
  Cookies.set(`${value}-authToken`, authToken, {
    expires: 1,
  });
  setCustomerInfo(authToken);
} else {
  if (authToken) { setInvalidToken(true); }
  throw {
    authToken,
    value,
  };
}

As you can see, this is more concise code, no repetition.