我如何使用递归 function 在 javascript 中推送数组

Question

I am trying to use the recursion function to push the data in the tempList, however no matter how to fix the code still is an empty array.

let tempList=[]
var getWineList =  function(database_name,locaDataBase){
    return new Promise(async (sucess,fail)=>{


        wineList(0,database_name)
        console.log(tempWineList)
        sucess("a")
    })
}

function wineList(currentPosition,database_name){

    let wines= db.collection(database_name)
    .skip(currentPosition)
    wines.get()
        .then((res)=>{


            // tempList.forEach(function(wine,index){
            //  tempWineList.push(wine)
            // })

            if(res.data.length<20){
                console.log(res.data)
                return res.data

            }
            tempWineList.push(res.data)
            return tempList.push(wineList(currentPosition+20,database_name))
        })


}

Answer 1

Method wines.get() is asynchronous. It means, that it don't returns value immediately, but it only returns a promise - promise that it will return value in future. In your code you push to an array inside then , so it won't be executed immediately, but when promise will be resolved, but inside getWineList function you don't wait for it to happen and execute console.log before that data is pushed.

So the solution is to return promise from wineList function and wait before doing console log. You can do it in 2 ways: by then() or async / await

Example of using async / await :

let tempList=[]
var getWineList =  async function(database_name,locaDataBase){
    await wineList(0,database_name)
    console.log(tempWineList)
    return "a";
}

function wineList(currentPosition,database_name){

    let wines = db.collection(database_name)
    .skip(currentPosition);

    let res = await wines.get();

    if(res.data.length<20){
        console.log(res.data)
        return res.data
    }
    tempWineList.push(res.data)
    return tempList.push(wineList(currentPosition+20,database_name))
})

}