ES6 Classes & Constructors

What OOP principle is demonstrated here?

class FormField {
  constructor(value = '') {
    this.value = value;
    this.errors = [];
  }
  
  setValue(value) {
    this.value = value;
    this.validate();
    return this;
  }
  
  validate() {
    this.errors = [];
    // Base validation logic
    return this.errors.length === 0;
  }
}

class EmailField extends FormField {
  validate() {
    super.validate();
    if (this.value && !this.value.includes('@')) {
      this.errors.push('Invalid email format');
    }
    return this.errors.length === 0;
  }
}

Encapsulation
Polymorphism
This code demonstrates polymorphism: 1) The child class overrides the validate method with its own implementation, 2) It extends the base functionality by calling super.validate(), 3) The same method name is used but with different behaviors in parent and child classes, 4) Code that uses FormField can work with EmailField without knowing the specific type, 5) This enables flexible and extensible code, 6) It's a key principle in object-oriented programming that allows for specialization while maintaining common interfaces.
Inheritance
Composition

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