It's common that a program has similar outlines for processing different targets with different detailed algorithms. Strategy Pattern encapsulates those algorithms and makes them interchangeable within the shared outline.

Consider conflicting merging processes of data synchronization, which we talked about in Chapter 2, The Challenge of Increasing Complexity. Before refactoring, the code was like this:

if (type === 'value') { 
  // ... 
} else if (type === 'increment') { 
  // ... 
} else if (type === 'set') { 
  // ... 
} 

But later we found out that we could actually extract the same outlines from different phases of the synchronization process, and encapsulate them as different strategies. After refactoring, the outline of the code became as follows:

let strategy = strategies[type]; 
strategy.operation(); 

We get a lot of ways to compose and organize those strategy objects or classes sometimes in JavaScript. A possible structure...