Node.js - Javascript - 返回异步变量

Question

I am working on a discord bot that will take random values from a Google Spreadsheet I have created. I have written my accessSpreadsheet.js file so that it will fetch data from Google Sheets, this is done asynchronously. I can console.log out the data I want from the async functions but I cannot set other variables by returning the asynchronous data, it instead returns undefined.

To start I have a discord.js that accepts input from Discord and calls my giRandom function and replys to the user with the output.

if(input === "!0"){
    var output = giRandom("1"); //this seed just guarantees a "true" outcome for  testing the boolSet function (located below)
    msg.reply(output); //Output's the returned giRandom data (currently replies but output is null)
}

Discord is calling the following function from giRandom.js Everything seems to work here until we reach var output = builder(seed_data);

//Returns a random number when fed a seed
function giRandom(seed) {

    //Seperate random seed js file. Working properly.
    var seedrandom = require('seedrandom');
    var rng = seedrandom(seed);

    var seed_Data = seedData(rng()); //Function below
    var output = builder(seed_Data); //Function below //Returning Undefined

    return output; //Returns output to discord.js (msg.reply(output))
}

exports.giRandom = giRandom; //located at end of file, not in a function

My giRandom function is calling seedData and builder functions (both located within giRandom.js)

seedData function

//Takes the seed generated by seedrandom (something like 0.1189181568115987) and seperates each digit into an array, ignoring NaN digits (in this case the decimal point)
function seedData(data){
    var counter = 0; //used to determine amount of NaN digits

    //Counts each NaN in inputArray
    var inputArray = Array.from(data.toString()).map(Number);
    for (var i = 0; i < inputArray.length; i++) {
        if (inputArray[i] >= 0) { //Checks for NaN
            if (debug) {
                console.log("inputArray[" + i + "] | " + inputArray[i]);
            }
        } else { //If NaN counter++
            counter++;
        }
    }

    var outputArray = new Array(counter); //Creates output array with correct size for all NaN values
    counter = 0; //Reset counter to 0

    //Creates outputArray containing all seed digits
    for (var i = 0; i < inputArray.length; i++) {
        if (inputArray[i] >= 0) {
            outputArray[counter] = inputArray[i];
            counter++;
        }
    }

    //Debug function to view output values
    for (var i = 0; i < outputArray.length; i++) {
        if (debug) {
            console.log("outputArray[" + i + "] | " + outputArray[i]);
        }
    }

    return outputArray; //returns outputArray to seed_Data in giRandom function
}

builder function

//Takes seed_Data from giRandom function and determines the value's output
function builder(data) {

    //Booleans, determine if each category returns a value based on boolSet() (function below)
    var raceBool;

    //data[0] is always a value of 0. 16 Total Usable values 1-17
    raceBool = boolSet(data[1]);


    if (raceBool == true) {
        var raceData = sheetToArray(1);
        console.log("raceData | " + raceData);
        return raceData; //Returning undefined
    }
}

My builder function is calling boolSet and sheetToArray functions (both located within giRandom.js)

boolSet function

//Each seed digit can be 0-9. If the digit passed (boolData) matches the value for valueTrue, valueFalse, or valuePick the output will be set accordingly. (Currently will always output True)
function boolSet(boolData) {
    var valueTrue = [0, 1, 2, 3];
    var valueFalse = [4, 5, 6, 7];
    var valuePick = [8, 9];

    //Loop through valueTrue and compare with boolData
    for (var i = 0; i <= valueTrue.length; i++) {
        if (boolData == valueTrue[i]) {
            if (debug) {
                console.log("boolData | " + boolData + " | true");
            }
            return true;
        }
    }

    //Loop through valueFalse and compare with boolData
    for (var i = 0; i <= valueFalse.length; i++) {
        if (boolData == valueFalse[i]) {
            if (debug) {
                console.log("boolData | " + boolData + " | false");
            }
            return false;
        }
    }
    //If !true && !false, must be "pick". This value will allow the end user to choose their data (in this case race)
    return "pick";
}

sheetToArray function

//takes an int for sheetNum that determines which sheet in the project to load 
function sheetToArray(sheetNum){
    var sheetArray = []; //Array that holds all rows of a particular worksheet, used to build spreadsheetArray
    var cellArray = []; //Array that holds all cells in a particular row of the worksheet used to build sheetArray
    var rowArrayCount = 1; //Counter to determine rows in cells forEach loop

    /*I believe this is where my problem probably lies*/
    //Calling async function accessSpreadsheet from spreadsheet.js
    accessSpreadsheet(sheetNum).then(function (arr) {
        var cells = arr;
        //loop through all cells in current sheet
        cells.forEach(cell => {
            if (cell.row > rowArrayCount) { //True determines that data is now on the next row of current sheet
                rowArrayCount++;
                sheetArray.push(cellArray); //push last row to sheetArray
                cellArray = []; //reset cellArray for new row
            }
            cellArray.push(cell._value); //push final row to cellArray
        })//Exit forEach
        sheetArray.push(cellArray); //push all rows to sheetArray
        var raceLength = sheetArray.length; //Returns value correctly
        console.log("raceLength | " + raceLength); //Returns value correctly
        console.log("sheetArray | " + sheetArray); //Returns value correctly
        return sheetArray; //Returns undefined
    })
}

To access Google Sheets I have a seperate js file. This is where the asynchronous function accessSpreadsheet() is

accessSpreadsheet.js

//Google Sheet Access Const
const GoogleSpreadsheet = require('google-spreadsheet');
const { promisify } = require('util');
const creds = require('./client_secret.json');
const doc = new GoogleSpreadsheet('**************'); //Google sheet we have access to (removed for security)

module.exports = accessSpreadsheet = async (sheetNum) => {
    await promisify(doc.useServiceAccountAuth)(creds);
    const info = await promisify(doc.getInfo)();
    const sheet = info.worksheets[sheetNum];

    //Async get sheet's cells without an offset
    const cells = await promisify(sheet.getCells)({
        offset: 0
    })

    return cells;
}

Answer 1

Basics of javascript promises :

accessSpreadsheet definition is something like

async accessSpreadsheet(args...){
   //Do stuff
   return something;
}

or like :

accessSpreadsheet(args...){
   return Promise(function (resolve,reject){
       // Do stuff
       resolve(return_value)
   })
}

Because of javascript being event-driven you cannot make it wait for i/o as it is detrimental to the user experience.

So you can solve your problem either by making all of your code async and using the await keyword to wait for accessSpreadsheet.

Like this :

await accessSpreadsheet()

which will wait for accessSpreadsheet to return before going to the next line.

This is a basic race condition scenario with promises.

You should remove vain promisification :

const info = await promisify(doc.getInfo)();

can be written :

const info = doc.getInfo();

and log the errors :

accessSpreadsheet(sheetNum).then(function (arr) {
   // somecode 
}).catch(console.error)

This will probably make your life easier