Node.js call back function on termination of a user defined function - node.js

Question

I have a node.js app consisting of a timer calling a user defined function made up of a bunch of functions in node language. The calling script has a timer calling function mybuy() every 10 seconds; mybuy() buys crypto currencies using Binance api according trigger prices contained in a mySQL table (alarms). I would like to start mysell() (not shown , but similar to myBuy()) right after mybuy() has run its course.
How to make mysell() the callback function of mybuy()?
This the calling script:
var fs = require('fs');
var sl = require('alberto/buy');
var loop = 0;
setImmediate(() => {
// start the log
fs.appendFile('./log.txt', "\n Loop-> " + loop + "\n", function (err) {
if (err) { console.log(err); }
})
//execute the function
sl.mybuy(); // USD function; everything happens here.Can take long to finish
var myInt = setInterval(function () {
loop++;
fs.appendFile('./log.txt', "Loop-> " + loop + "\n", function (err) {
if (err) { console.log(err); }
})
//execute every 10 secs
sl.mybuy();
if (loop > 5) { clearInterval(myInt); } // max 6 loops for testing
}, 10000);
});
the UDF id here
exports.mybuy = function () {
var fs = require('fs'); // I keep a log.txt
process.stdout.write("\u001b[2J\u001b[0;0H");// clear screen
aww = (new Date()).toJSON().slice(0, 19).replace(/[-T]/, '-');
aww = aww.replace(/T/, ' ');
console.log(aww, '\n\n'); // practicing with dates
var mysql = require('mysql');
var con = mysql.createConnection({
host: "www.photobangkok.com",
user: "photoban_user",
password: "xxxxxxxx",
database: "photoban_datab"
});
// 'added' is for never processed entries in alarms table.It will change to BOUGHT or SOLD
sql = "SELECT rec, id,coin,buy,amount_b,stat FROM alarms where stat='added' AND buy>0 order by coin";
var cnt = 0; // not used, perhaps an idea to emit an event when cnt reaches the number of rows
con.query(sql, function (err, result) {
if (err) throw err;
str = "";
for (var index in result) {
str = result[index].rec + "-" + result[index].id + "-" + result[index].coin + "-" + result[index].buy + "-" + result[index].amount_b + "-" + result[index].stat;
// set up variables
coin = result[index].coin;
buy = result[index].buy;
rec = result[index].rec;
id = result[index].id;
amount = result[index].amount_b;
console.log('\x1b[36m%s\x1b[0m', str); // set color green. Display str
checkprice(coin, buy, rec, id, amount); //check Binance today price for the coin.The function will execute sometimes
} // end of loop
console.log('\x1b[36m%s\x1b[0m', str); // set color green. Display str
});
//check single coin price using binance api
function checkprice(coin, buy, rec, id, amount) {
const binance = require('node-binance-api')().options({
APIKEY: '<key>',
APISECRET: '<secret>',
useServerTime: true,
test: true //sandbox does not work
});
binance.prices(coin, (error, ticker) => {
act = "Nothing"; // default value
pricenow = ticker[coin]; // note ticker[coin]
if (pricenow < buy) {
show(id, rec, coin, buy, amount, pricenow);// Display sometimes then call book()
} else { console.log(coin, pricenow, buy, act, '\n'); }
});
}
function show(id, rec, coin, buy, amount, pricenow) {
delta = buy - pricenow; // posted trigger - today price
delta = delta.toFixed(8);
console.log('\x1b[31m%s\x1b[0m', coin, buy, amount, id, rec, ">BUY", delta); //display entries from alarms higher that today price
book(id, rec, coin, buy, amount, pricenow);
}
// dummy function to be replaced with a buy api order
function book(id, rec, coin, buy, amount, pricenow) {
const binance = require('node-binance-api')().options({
APIKEY: '<key>',
APISECRET: '<secret>',
useServerTime: true,
test: true //sandbox
});
console.log("Order:buy what??", coin, "amount:", amount, '\n');
/* binance.prices(coin, (error, ticker) => {
console.log("booking",coin, ticker[coin]);
update(id,rec);
}); */
update(id, rec, amount); // update mySql table. Slow but sure
}
function update(id, rec, amount) {
var sql = "UPDATE alarms SET stat = 'BOUGHT' ,today =
CONVERT_TZ(now(), '+00:00', '+7:00') WHERE id = "+id+" AND rec = "+rec;
con.query(sql, function (err, result) {
if (err) throw err;
console.log(result.affectedRows + " record updated");
// keep a log.tx
fs.appendFile('./log.txt', aww + " bought " + id + "-" + rec + "-" + amount + "\n",
function (err) {
if (err) { console.log(err); }
})
});
}
// I could check if all rows are done and raise an event? (how to do it)
} // end

Answer 1

To make mySell as the callback method of myBuy, invoke the myBuy method using the following structure.
myBuy(() => {
// operation of mySell method
});
And your myBuy method should return the callback, after perform its own operation.
exports.myBuy = function(cb) {
// operation of myBuy method
return cb; // return to the mySell method
}