编辑代码

const data = [
    {date:'2021-12-25',cnt:12},
    {date:'2021-12-28',cnt:7},
    {date:'2021-12-30',cnt:9},
    {date:'2022-01-02',cnt:4},
    {date:'2021-01-03',cnt:4},
]

function pathDate(data){
    let startTime = (data[0].date).split("-")
    let endTime = (data[data.length-1].date).split("-")

    let sumDate = new Date(startTime[0],startTime[1],0).getDate()

    let dataArray = []
    //12月
    for(let i = Number(startTime[2]) ; i<= sumDate ; i++){
        let lableName = startTime[0]+"-"+startTime[1] +"-"+ i
        let isExist = data.filter((item)=>{return item.date==lableName})
        if(isExist && isExist.length>0){
            dataArray.push(isExist[0])
        }else{
            dataArray.push({
                date:lableName,
                cnt:0
            })
        }
    }
//1月
    for(let i = 1 ; i<= Number(endTime[2]); i++){
        let lableName = endTime[0]+"-"+endTime[1] +"-0"+ i
        let isExist = data.filter((item)=>{return item.date==lableName})
        if(isExist && isExist.length>0){
            dataArray.push(isExist[0])
        }else{
            dataArray.push({
                date:lableName,
                cnt:0
            })
        }
    }
    console.log(dataArray)

}
pathDate(data)