How to add new property to json object when using JSON.stringify

For example, now there is a json object called jsonObj, you need to add a new attribute newParam to this object, and assign the value new to newParam. The method is as follows:

var jsonObj={
'param1': 111,
'param2': 222
};

Add new attribute: newParam = 'new

jsonObj. newParam ='new';

After the new attribute is added, the json object becomes:

var jsonObj={
'param1': 111,
'param2': 222,
'newParam':'new'
};

---

Application in actual scenarios, for example, I need a jump with parameters:

    // 立即购买
            confirmBuy() {
                this.show = false;
                uni.navigateTo({
                    url: "/pages/settlecenter/settlecenter?goods=" +
                        JSON.stringify(this.optitem),
                });
            },

The json structure that needs to be passed is as follows: this.optitem

optitem: [{
                        StockNum: "497",
                        articleId: "9066",
                        goods_xl: "5",
                        hasRelated: "1",
                        images: [{
                                id: '001',
                                Path: ["https://xxx/images/myIcon/recommend1.png"],
                            },
                            {
                                id: '002',
                                Path: ["https://xxx/images/myIcon/recommend1.png"],
                            }

                        ],
                        isInStock: "1",
                        isStock: "1",
                        markingPrice: "450.00",
                        name: "示例商品1",
                        original_price: "450.00",
                        price: "410.00",
                        price_mh: "",
                        unitPrice: "410.00",
                    },

Now you need to add a new attribute count to the above json object, written as [ this.optitem.count = e.value ]

// 购物车的数值发生改变
            changeNumberBox(e) {
                console.log("值发生改变 ", e.value);    
                // 添加新属性
                this.optitem.count = e.value            
                // this.count = e.value
                console.log("548",this.optitem);
}