use deep copy

index.ts

@@ -23,7 +23,10 @@ export default class YGOProDeck implements YGOProDeckLike {
   name?: string;
 
   constructor(init: Partial<YGOProDeckLike> = {}) {
-    Object.assign(this, init);
+    this.main = init.main ? [...init.main] : [];
+    this.extra = init.extra ? [...init.extra] : [];
+    this.side = init.side ? [...init.side] : [];
+    this.name = init.name;
   }
 
   bufferLength(noCompact = false) {

tests/deep-copy.spec.ts

+import YGOProDeck from '..';
+
+describe('Constructor deep copy', () => {
+  it('should deep copy main/extra/side arrays from plain object', () => {
+    const init = {
+      main: [1, 2],
+      extra: [3],
+      side: [4, 5],
+    };
+
+    const deck = new YGOProDeck(init);
+
+    expect(deck.main).toStrictEqual([1, 2]);
+    expect(deck.extra).toStrictEqual([3]);
+    expect(deck.side).toStrictEqual([4, 5]);
+
+    expect(deck.main).not.toBe(init.main);
+    expect(deck.extra).not.toBe(init.extra);
+    expect(deck.side).not.toBe(init.side);
+
+    init.main.push(99);
+    init.extra.push(88);
+    init.side.push(77);
+
+    expect(deck.main).toStrictEqual([1, 2]);
+    expect(deck.extra).toStrictEqual([3]);
+    expect(deck.side).toStrictEqual([4, 5]);
+
+    deck.main.push(66);
+    deck.extra.push(55);
+    deck.side.push(44);
+
+    expect(init.main).toStrictEqual([1, 2, 99]);
+    expect(init.extra).toStrictEqual([3, 88]);
+    expect(init.side).toStrictEqual([4, 5, 77]);
+  });
+
+  it('should deep copy main/extra/side arrays from another deck', () => {
+    const source = new YGOProDeck({
+      main: [10],
+      extra: [20, 21],
+      side: [30],
+      name: 'source',
+    });
+
+    const deck = new YGOProDeck(source);
+
+    expect(deck.main).toStrictEqual([10]);
+    expect(deck.extra).toStrictEqual([20, 21]);
+    expect(deck.side).toStrictEqual([30]);
+
+    expect(deck.main).not.toBe(source.main);
+    expect(deck.extra).not.toBe(source.extra);
+    expect(deck.side).not.toBe(source.side);
+
+    source.main.push(11);
+    source.extra.push(22);
+    source.side.push(31);
+
+    expect(deck.main).toStrictEqual([10]);
+    expect(deck.extra).toStrictEqual([20, 21]);
+    expect(deck.side).toStrictEqual([30]);
+
+    deck.main.push(12);
+    deck.extra.push(23);
+    deck.side.push(32);
+
+    expect(source.main).toStrictEqual([10, 11]);
+    expect(source.extra).toStrictEqual([20, 21, 22]);
+    expect(source.side).toStrictEqual([30, 31]);
+  });
+});