Open-Closed Principle (OCP) - SOLID

The SOLID Principles

• 🧱
  Single Responsibility Principle (SRP) - SOLID

• 🧱
  Open-Closed Principle (OCP) - SOLID

• 🧱
  Liskov Substitution Principle (LSP) - SOLID

• 🧱
  Interface Segregation Principle (ISP) - SOLID

• 🧱
  Dependency Inversion Principle (DIP) - SOLID

The Open-Closed Principle (OCP)

Benefits Explained

• Minimizes changes: You only need to add things when you need to extend a class.

• Working code is not affected: It’s harder to break things because changes in existent classes are not needed.

Example

BAD

// BAD
class AjaxAdapter extends Adapter {
  constructor() {
    super();
    this.name = "ajaxAdapter";
  }
}

class NodeAdapter extends Adapter {
  constructor() {
    super();
    this.name = "nodeAdapter";
  }
}

class HttpRequester {
  constructor(adapter) {
    this.adapter = adapter;
  }

  fetch(url) {
    if (this.adapter.name === "ajaxAdapter") {
      return makeAjaxCall(url).then(response => {
        // transform response and return
      });
    } else if (this.adapter.name === "nodeAdapter") {
      return makeHttpCall(url).then(response => {
        // transform response and return
      });
    }
  }
}

function makeAjaxCall(url) {
  // request and return promise
}

function makeHttpCall(url) {
  // request and return promise
}

GOOD

class AjaxAdapter extends Adapter {
  constructor() {
    super();
    this.name = "ajaxAdapter";
  }

  request(url) {
    // request and return promise
  }
}

class NodeAdapter extends Adapter {
  constructor() {
    super();
    this.name = "nodeAdapter";
  }

  request(url) {
    // request and return promise
  }
}

class HttpRequester {
  constructor(adapter) {
    this.adapter = adapter;
  }

  fetch(url) {
    return this.adapter.request(url).then(response => {
      // transform response and return
    });
  }
}