Pfthb

I am reading a DB and output the result in a string.
The issue is that sometimes the output is empty, my guess is that the function "json" is executed before the DB-read is completed.. I tried to apply "callback" which I read in other threads, but it didnt solve it.
What am I doing wrong?

var response = ;
var items = ;
var table = "table";

exports.handler = async (event) => 
ReadDB(json);
return response;
;

//**********************ReadDB Function
function ReadDB(callback) 
var paramsRead = 
 TableName: table,
;

// Call DB to read the item from the table
ddb.scan(paramsRead, function(err, data) 
 if (err) 
 console.log("Error reading DynamoDB", err);
 else 
 items = data.Items;
 
);

callback(items);



//**********************json Function
function json(items) 
 console.log(items);
 response = 
 body: JSON.stringify(items, null, 't'),
 ;
 console.log(response);

Yes, This is called asynchronious. This is the relevant bit:

// Call DB to read the item from the table
ddb.scan(paramsRead, function(err, data) 
 if (err) 
 console.log("Error reading DynamoDB", err);
 else 
 items = data.Items;
 
);

callback(items);

You likely expect that ddb.scan() fires and completes, then callback(). But the scan function is async, which (simply put) it doest block the remaining code.

You should read this code as: ddb.scan() is started and then then callback() is started. The .scan() is practically always slower, thus no result.

In your example, you have the data in your else, this is where you trigger callback(data.Item), as that code is on the revolve of the .scan() function.

Promises are a tricky concept to wrap your head around in the beginning, I suggest you do some research. Controling promises is difficult in the beginning, but understanding the basics is doable.

Suggested reading material I found by Googling "javascript simple promises explanation"