Template Method Design Pattern Explained

The Template Method pattern defines the skeleton of an algorithm in a base class and lets subclasses override specific steps without changing the overall order.

The concept

The base method calls a fixed sequence: step1(), step2(), step3(). Some steps are abstract or have default implementations that subclasses override.

It enforces a consistent workflow while allowing variation, such as report generation or data import pipelines.

Fixed order, customisable steps

Practical examples

Base class

class Importer {
  run() { const d = this.read(); const t = this.transform(d); this.save(t) }
  transform(d) { return d }
  read() { throw new Error('implement') }
  save() { throw new Error('implement') }
}

Subclass

class CsvImporter extends Importer {
  read() { return readCsv('in.csv') }
  save(rows) { db.insert(rows) }
}
new CsvImporter().run()

Hook method

class A { run() { this.before?.(); this.work(); this.after?.() } }

Common mistakes

• Too many overridable steps.
• Subclasses calling steps in a different order.
• Preferring inheritance when composition (Strategy) is simpler.

Key takeaways

• Skeleton in base, steps in subclasses.
• Fixed order.
• Consider Strategy as an alternative.

FAQ

Template Method vs Strategy?

Template uses inheritance; Strategy uses composition.

Where is it common?

Frameworks with lifecycle hooks, like test runners.