jquery regroups the arrays with the same year and month into a new array

//Original array
 var data = {

    results: [{
        id:0,
        date:'2017-12-12',
        content:'123'
    },{
        id:0,
        date:'2017-12-12',
        content:'123'
    },{
        id:0,
        date:'2017-11-12',
        content:'123'
    },{
        id:0,
        date:'2018-04-12',
        content:'123'
    }],
    totalSize: 46,
    validNumber: 0
}

var data2 = {};
var arr = [];
var keyMap = {};
for (var i = 0; i < data.results.length; i++) {
    var arrElem = data.results[i];
    var elemKey = arrElem.date.substring(0, 7);// Intercept the year and month
    if (elemKey in keyMap) {
        arr[keyMap[elemKey]].value.push(arrElem);
    } else {
        arr.push({
            "date": arrElem.date.substring(0, 7),
            "value": [arrElem]
        });
        keyMap[elemKey] = arr.length - 1;
    }
}
data2 = {
    results:arr,
    totalSize: 46,
    validNumber: 0
}
console.log(data2);

//处理后的结果

var data2 = {
    results: [{
        date:'2017-12',
        value:[{
            id:0,
            date:'2017-12-12',
            content:'123'
        },{
            id:0,
            date:'2017-12-12',
            content:'123'
        }],
    },{
        date:'2017-11',
        value:[{
            id:0,
            date:'2017-11-12',
            content:'123'
        }],
    },{
        date:'2018-04',
        value:[{
            id:0,
            date:'2018-04-12',
            content:'123'
        }],
    }],
    totalSize: 46,
    validNumber: 0
}