JS合并数组对象中重复数据[通俗易懂]

// 源数据
var oldData = [
{ 

city_id: 1,
city_name: '北京',
city_img: "http://dfknbdjknvkjsfnvlkjdn.png",
city_country: "中国"
},
{ 

city_id: 2,
city_name: '上海',
city_img: "http://wergerbe.png",
city_country: "中国"
},
{ 

city_id: 3,
city_name: '广州',
city_img: "http://hrthhr.png",
city_country: "中国"
},
{ 

city_id: 4,
city_name: '西雅图',
city_img: "http://frevfd.png",
city_country: "美国"
},
{ 

city_id: 5,
city_name: '纽约',
city_img: "http://反而个.png",
city_country: "美国"
}
]
// 把源数据先变成目标数据的规则
var oldDataRule = []
oldData.forEach(el => { 

var oldObj = { 

name: el.city_country,
citys:[]
}
var cityObj = { 

city_name: el.city_name,
city_img: el.city_img,
city_id: el.city_id
}
oldObj.citys.push(cityObj)
oldDataRule.push(oldObj)
})
/** * 先去重，后合并 * 1、源数据去重 * 2、把去重后的数据和源数据中相同name的数据合并citys */
var newData = []
var newObj = { 
}
oldDataRule.forEach((el, i) => { 

if (!newObj[el.name]) { 

newData.push(el);
newObj[el.name] = true;
} else { 

newData.forEach(el => { 

if (el.name === oldDataRule[i].name) { 

el.citys = el.citys.concat(oldDataRule[i].citys);
// el.citys = [...el.citys, ...oldDataRule[i].citys]; // es6语法
}
})
}
})
console.log(newData); // 目标数据