Why is this an issue?

A selector parameter is a boolean parameter that’s used to determine which of two paths to take through a method. Specifying such a parameter may seem innocuous, particularly if it’s well named.

Unfortunately, developers calling the method won’t see the parameter name, only its value. They’ll be forced either to guess at the meaning or to take extra time to look the method up.

This rule finds methods with a boolean that’s used to determine which path to take through the method.

Noncompliant code example

function tempt(name: string, ofAge: boolean) {
  if (ofAge) {
    offerLiquor(name);
  } else {
    offerCandy(name);
  }
}

// ...
function corrupt() {
  tempt("Joe", false); // does this mean not to temp Joe?
}

Compliant solution

Instead, separate methods should be written.

function temptAdult(name: string) {
  offerLiquor(name);
}

function temptChild(name: string) {
  offerCandy(name);
}

// ...
function corrupt() {
  age < legalAge ? temptChild("Joe") : temptAdult("Joe");
}