如何将下列数组中key相同的对象组成新的数组

var a=[{name:1,key:'a'},{name:2,key:'b'},{name:3,key:'a'},{name:3,key:'b'}]

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var b = {};
$.each(arr, function (i,v){
    var g = v[keyName],
        c = b[g];
    if(c){
        b[g].push(v);
    }else{
        b[g] = [v];
    };
});

---

var b = {};
a.forEach(function (obj) {
    var array = b[obj['key']] || [];
    array.push(obj);
    b[obj['key']] = array;
});
console.log(b.a.length);
console.log(b.b.length);

---

var b = a.reduce(function(v, k) {
    var filters = v.filter(function(data) {
        return data.key === k.key
    });
    if (filters.length === 0) {
        v.push({
            key: k.key,
            name: [k.name]
        })
    } else {
        filters[0].name.push(k.name)
    };
    return v
}, [])

console.log(b)
//[{"key":"a","name":[1,3]},{"key":"b","name":[2,3]}]

---

//var a =........;
var result = new Array();
for(var index in a){
 result[a[index].key] = new Array();
 result[a[index].key].push(a[index]);
}
console.log(result);

这是个简单但经典的问题。for in属于js语法，请自行搜索参考资料。

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https://lodash.com/docs#groupBy