Using Proxy and Reflect (ES6) to restrict insertion of objects into an Array - with test

proxy.js

"use strict";

class Fruit {
    constructor(name){
        this._name = name;
    }

    set name(name){
        this._name = name;
    }

    get name(){
        return this._name;
    }
}

class Vegetable {
    constructor(name){
        this.name(name);
    }

    set name(name){
        this._name = name;
    }

    get name(){
        return this._name;
    }
}

// a proxy for our array
var fruitbowl = new Proxy([], {
    deleteProperty: function(target, property) {
        return true;
    },
    set: function(target, property, value, receiver) {
        //console.log("Setting "+property+" to ",value);
        if(property == "length"){
          target.length = value;
          return true;
        } else {
          if(value instanceof Fruit){
              target[property] = value;
              return true;
          } else {
            return false;
            throw TypeError("Expected Fruit, got "+typeof(value)+" ("+value+")");
          }
        }
    }
});

Reflect.defineProperty(fruitbowl, 'splice', {
  configurable: true,
  enumerable: false,
  value: function(start, deleteCount, ...items) {
    if (items.every(item => item instanceof Fruit)) {
      return Reflect.apply(Array.prototype.splice, this, [start, deleteCount, ...items]);
    } else {
      throw new Error('All elements must be Fruit objects');
    }
  }
});

console.log("\n\n=== Putting fruit into the bowl... ===\n\n");

try{
  fruitbowl.push(new Vegetable("potato"));
} catch (e){
  console.log("Shoudln't allow vegetables: PASSED");
}
console.log("Fruitbowl should still be empty: " + (fruitbowl.length == 0 ? "PASSED" : "FAILED"));

fruitbowl.push(new Fruit("apple"));
console.log("Should allow fruit: " + (fruitbowl.length == 1 ? "PASSED" : "FAILED"));

fruitbowl[0] = new Fruit("orange");
console.log("Should replace item specified as long as it's a Fruit: " + (fruitbowl.length == 1 && fruitbowl[0].name == "orange" ? "PASSED" : "FAILED"));

try {
  fruitbowl[0] = "Bananas!!1one";
} catch(e) {
  
}
console.log("Should not replace with a string: " + (fruitbowl.length == 1 && fruitbowl[0].name == "orange" ? "PASSED" : "FAILED"));

fruitbowl.push(new Fruit("banana"), new Fruit("pear"));
console.log("Should have 3 items [orange, banana, pear]: " + (fruitbowl.length == 3 ? "PASSED" : "FAILED"), fruitbowl);

console.log("\n\n === Cropping the bowl... ===\n\n");

fruitbowl.length = 2;
console.log("Should have 2 items [orange,banana]: " + (fruitbowl.length == 2 ? "PASSED" : "FAILED"));
console.log("Should error at item 2: " + (!fruitbowl[2] ? "PASSED" : "FAILED"), fruitbowl);

console.log("\n\n === Splicing the bowl... ===\n\n");

try{
  fruitbowl.splice(0,0,"pineapples!!1one");
console.log(fruitbowl.length);
} catch (e){
  console.log("Shouldn't have inserted string: PASSED");
}
console.log("Should still only have 2 fruit: " + (fruitbowl.length == 2 ? "PASSED" : "FAILED ("+fruitbowl.length+")"));

fruitbowl.splice(0,0,new Fruit("pineapple"));
console.log("Should now have 3 fruit: " + (fruitbowl.length == 3 ? "PASSED" : "FAILED"));
console.log("Should first fruit should be pineapple: " + (fruitbowl[0].name == "pineapple" ? "PASSED" : "FAILED"));

fruitbowl.splice(1,1);
console.log("Should now have 2 fruit: " + (fruitbowl.length == 2 ? "PASSED" : "FAILED"));
console.log("Should first fruit should be pineapple: " + (fruitbowl[0].name == "pineapple" ? "PASSED" : "FAILED"));
console.log("Should second fruit should be banana: " + (fruitbowl[1].name == "banana" ? "PASSED" : "FAILED"));
console.log("Should third fruit should be non-exostant: " + (typeof(fruitbowl[2] )== "undefined" ? "PASSED" : "FAILED"));