合并数组对象中相同的属性值

var arr = [{
        "name": "语文",
        "fraction": 80
    }, {
        "name": "数学",
        "fraction": 70
    }, {
        "name": "语文",
        "fraction": 50
    }, {
        "name": "语文",
        "fraction": 90
    }, {
        "name": "数学",
        "fraction": 100
    }, {
        "name": "数学",
        "fraction": 55
    }, {
        "name": "语文",
        "fraction": 99
    }]

var res =[];
var narr=[];
    for(var i =0;i<arr.length;i++){
        var n = res.indexOf(arr[i].name);
    if(n == -1){
        res.push(arr[i].name);
        narr.push({"name":arr[i].name,fraction:[arr[i].fraction]})
        }else{
        narr[n].fraction.push(arr[i].fraction)
        }
    }
console.log(narr)
输出结果：
[{
    "name": "语文",
    "fraction": [80, 50, 90, 99]
}, {
    "name": "数学",
    "fraction": [70, 100, 55]
}, {
    "name": "英语",
    "fraction": [55, 89]
}]

arr = arr.map(function(item, index, arr) {
    const i = arr.find(_item => item.name === _item.name);
    if(i !== item) {
        i.fraction.push(item.fraction);
        return undefined;
    } else {
        i.fraction = [i.fraction];
        return i;
    }
}).filter(item => item !== undefined);
输出结果：
[{
    "name": "语文",
    "fraction": [80, 50, 90, 99]
}, {
    "name": "数学",
    "fraction": [70, 100, 55]
}, {
    "name": "英语",
    "fraction": [55, 89]
}]