How to reduce cognitive complexity of nested if

Question

I have an if statement set up like this

if (A && B) {
   // do something 1
} else {
   if (B) {
      // set some boolean to false
   } 
   // do something 2
}

I'm wondering if I can lower the cognitive complexity? Right now this is a score of 4.

Answer 1

I would say the best way to lower the cognitive complexity is to use functions. This is similar to @GuerricP original answer, but handles the multiple case of do somthing 2

eg.

function doSomething2() {}

if (A && B) {
  // do something 1
} else if (B) {  
  // set some boolean to false
  doSomething2();
} else {
  doSomething2();
}

This reduces complexity, because it's not obvious that there are 2 routes to doSomething2 in your original version.

Answer 2

Well you could have only one level of depth like this:

function originalImplementation(A, B) {
  if (A && B) {
    console.log("do something 1");
  } else {
    if (B) {
      console.log("set some boolean to false");
    }
    console.log("do something 2");
  }
}

function newImplementation(A, B) {
  if (A && B) {
    console.log("do something 1");
  }
  else if (B) {
    console.log("set some boolean to false");
  }
  if (!A || !B) {
    console.log("do something 2");
  }
}

console.log("originalImplementation");

originalImplementation(0, 0);
originalImplementation(0, 1);
originalImplementation(1, 0);
originalImplementation(1, 1);

console.log("newImplementation");

newImplementation(0, 0);
newImplementation(0, 1);
newImplementation(1, 0);
newImplementation(1, 1);

Answer 3

Setting the boolean first can setup a clearer if/else

if(!A && B) {
  // set some boolean to false
}

if (A && B) {
  // do something 1
} else {
  // do something 2
} 

Another strategy is to drop out of functions asap

e.g.

if(X) {
  // do stuff

  return;
} 

if(Z)
{
  // do different stuff
  return; 
}

// do default stuff
return;

This allows the reader to dismiss logic beyond the condition they are interested in

Finally you can also create functions with meaningful names rather than comments

if(X) {
  return doSomething2();
} 

Answer 4

I think this is the right way to do it and the cleanest.

const DoSomething = function(){}

if (A && B) {
} 
else if (B) {  
DoSomething();
} 
else {
 DoSomething();
}

Answer 5

Assuming you do one and only one thing for each case you can try decluttering the syntax:

1. One-liner if statements don't need the curly braces
2. You can avoid if, else if, etc. with an early return

const run = (a, b) => {
  if (a && b) return fun1();
  if (a) return fun2();
  if (b) return fun3();
  return fun4();
}

In this case I prefer using nested ternaries. Something usually considered as "bad practice" by tool makers and opinion leaders in the industry but I think with the right indentation they offer more decluttering opportunities:

const run = (a, b) =>
  ( a && b ? fun1()
  : a      ? fun2()
  : b      ? fun3()
           : fun4());

Of course YMMV ;)