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Strategy Pattern

Strategy Pattern

Introduction

The Strategy pattern defines a family of interchangeable algorithms and lets you choose which one to use at runtime.

Topics Covered

Implementation — Interchangeable algorithm families
Real-World Examples — Form validation, sorting, payment processing

Implementation

// Strategies
const strategies = {
  add: (a, b) => a + b,
  subtract: (a, b) => a - b,
  multiply: (a, b) => a * b,
  divide: (a, b) => a / b
};

// Context
function calculate(strategy, a, b) {
  if (!strategies[strategy]) throw new Error('Unknown strategy');
  return strategies[strategy](a, b);
}

calculate('add', 5, 3);      // 8
calculate('multiply', 5, 3); // 15

// Form validation example
const validators = {
  required: value => value.trim() !== '' ? null : 'Required',
  email: value => /^.+@.+$/.test(value) ? null : 'Invalid email',
  minLength: min => value => value.length >= min ? null : `Min ${min} chars`
};

function validate(field, value, rules) {
  for (const rule of rules) {
    const error = validators[rule] ? validators[rule](value) : rule(value);
    if (error) return { field, error };
  }
  return null;
}

Summary

Selects algorithm at runtime
Avoids long if/else chains
Each strategy is independently testable

Further Reading

Refactoring Guru: Strategy