数组嵌套对象，将相同属性去重，对应的某个属性值合并

var data = [
    { province: 1, index:1},
    { province: 2, index:3},
    { province: 1, index:3},
    { province: 2, index:2}
]

function mergeArr(arr){
    var newArr=[];
        arr.forEach(item=>{
        var dataItem =item
            if(newArr.length>0){
                var filterValue = newArr.filter(v=>{
                   return v.province == dataItem.province
                })
                if(filterValue.length>0){
                    newArr.forEach(n=>{
                       if( n.province ==filterValue[0].province){
                           n.index =  Number(filterValue[0].index) + Number(dataItem.index)
                       } 
                    })
                }else{
                    newArr.push(dataItem)
                }
            }else{
                newArr.push(dataItem)
            }
    
    })
    return newArr
    }