[ Wrong ] - Open / Closed Principle

wrong-ocp.js

class Pdf {
  constructor(name, size) {
    this.name = name;
    this.size = size;
  }

  // ...
}
class Png {
  constructor(name) {
    this.name = name;
  }

  // ...
}
class Printer {
  function printFile(file) {
    if (file instanceof Pdf) {
      // Print Pdf...
    } else if (file instanceof Png) {
      // Print Png...
    }
  }
}