Refactoring Simplifying Method Calls

2. Manage Logic and Parameters

• Separate Query from Modifier: Split methods that both return a value and change an object's state. One method should be a "Query" (no side effects) and the other a "Modifier."
• Parameterize Method: If multiple methods do similar things with different values, combine them into one method that accepts those values as parameters.
• Replace Parameter with Explicit Methods: If a method's behavior is dictated by a flag/parameter, split it into separate, explicitly named methods (e.g., setHeight(val) instead of setValue('height', val)).
• Preserve Whole Object: Instead of extracting several values from an object to pass as parameters, pass the entire object to simplify the call.
• Introduce Parameter Object: If a group of parameters is repeatedly passed together, replace them with a single object (e.g., DateRange instead of separate start and end dates).

3. Improve Object Creation and Error Handling

• Replace Constructor with Factory Method: Use a static factory method if the construction logic is complex or needs to return different subclasses.
• Replace Error Code with Exception: Instead of returning special error values (like -1), throw specific exceptions to separate normal execution flow from error handling.
• Replace Exception with Test: If an exception is being used for a case that can be easily checked with a simple conditional, use the test instead.

TypeScript Examples

Separate Query from Modifier (CQRS)

// BEFORE: Method gets data AND changes state (side effect)
getTotalOutstandingAndSetReady(): number {
  this.isReady = true;         // Modifier
  return this.calculateTotal(); // Query
}

// AFTER: Responsibilities split
getTotalOutstanding(): number {
  return this.calculateTotal();
}
setReady(): void {
  this.isReady = true;
}

Introduce Parameter Object

// BEFORE: Repeating group of parameters
amountInvoicedIn(start: Date, end: Date): number { /* ... */ }
amountOverdueIn(start: Date, end: Date): number { /* ... */ }

// AFTER: Parameters grouped into an immutable object
class DateRange {
  constructor(
    public readonly start: Date,
    public readonly end: Date
  ) {}
}

amountInvoicedIn(range: DateRange): number { /* ... */ }
amountOverdueIn(range: DateRange): number { /* ... */ }

Replace Error Code with Exception

// BEFORE: Returning special values for errors
withdraw(amount: number): number {
  if (amount > this.balance) return -1;
  this.balance -= amount;
  return 0;
}

// AFTER: Using proper exception handling
withdraw(amount: number): void {
  if (amount > this.balance) {
    throw new InsufficientFundsError();
  }
  this.balance -= amount;
}

Payoff

• Intuitive API: Method names and signatures clearly communicate intent.
• Reduced Coupling: Passing objects or parameter objects makes signatures more resilient to changes.
• Clean Flow: Separating queries from modifiers and using exceptions instead of error codes results in much cleaner calling code.