Interpreter

Interpreter pattern is used to convert one representation of a data into another. This type of pattern comes under behavioral pattern. It uses a class to represent the given language. This pattern involves implementing an expression interface which tells to interpret a particular context. It is usually used in the cases where we have a class that invokes its method on the runtime value and we don't know the exact type of the class. In the implementation of the expression interface, just check the class of the object and then convert the object into a different object.

class Expression {
  constructor(expression) {
    this.expression = expression;
  }

  interpret(context) {
    if (context.split(" ").indexOf(this.expression) != -1) {
      return true;
    }
    return false;
  }
}

class TerminalExpression extends Expression {
  constructor(data) {
    super(data);
  }

  interpret(context) {
    let result = context.split(" ").indexOf(this.expression);
    if (result != -1) {
      return true;
    }
    return false;
  }
}

class OrExpression extends Expression {
  constructor(expr1, expr2) {
    super();
    this.expr1 = expr1;
    this.expr2 = expr2;
  }

  interpret(context) {
    return this.expr1.interpret(context) || this.expr2.interpret(context);
  }
}

class AndExpression extends Expression {
  constructor(expr1, expr2) {
    super();
    this.expr1 = expr1;
    this.expr2 = expr2;
  }

  interpret(context) {
    return this.expr1.interpret(context) && this.expr2.interpret(context);
  }
}

function getMaleExpression() {
  let robert = new TerminalExpression("Robert");
  let john = new TerminalExpression("John");
  return new OrExpression(robert, john);
}

function getMarriedWomanExpression() {
  let julie = new TerminalExpression("Julie");
  let married = new TerminalExpression("Married");
  return new AndExpression(julie, married);
}

let isMale = getMaleExpression();
let isMarriedWoman = getMarriedWomanExpression();

console.log("John is male? " + isMale.interpret("John"));
console.log("Julie is a married women? " + isMarriedWoman.interpret("Married Julie"));