How to access a local variable from outside the function in node.js

Question

All I am trying here is to access the local variable 'htmlrows' outside the function but it seems its not that easy with node.js.

var htmlrows;
query.on('row', function(row) {    
  console.log("%s  |%s |%d",    row.empid,row.name,row.age); 
  htmlrows += "<tr><td>" + row.empid + "</td><td>" +row.name + "</td><td>" +row.age + "</td></tr>";

});

console.log("htmlrows outside function");
console.log(htmlrows); // console log prints 'undefined'.

Could you please let me know how to access 'htmlrows' outside the function?

Thanks much in advance

Why not apply the logic inside the function, where the result is returned? — Ben Fortune
– Ben Fortune, Commented Jun 17, 2014 at 9:52
Thanks Ben for the quick response. As you said rightly that is a possibility but I would like to access is outside the function.Just for my learning if I really wanted to access outside the function how would i do it? — user3747813
– user3747813, Commented Jun 17, 2014 at 10:03
Assuming there's an end event in the instance of EventEmitter which is query (this is typical): query.on('row',function(row){...htmlrows += "...";}).on('end',function(){console.log(htmlrows);}); — zamnuts
– zamnuts, Commented Jun 17, 2014 at 10:07

Stephen Wright · Accepted Answer · 2014-06-17 10:04:05Z

Your issue is that node.js is asynchronous, so console.log(htmlrows); is being executed before the query function has completed.

What you need to do is have a separate function that listens for a callback from the query function.

You could try using the async middleware for node.js, which will allow you to chain async calls in series, so that they get executed in a certain order:

var some_data = null;
async.series([
    function(callback) {
      //...do a thing
      function_1(callback);
    },
    function(callback) {
      //...do another thing
      function_2(callback);
    }
    //...etc
]);

function function_1(callback) {
    some_data = 'value';
    console.log('function_1!');
    return callback();
}

function function_2(callback) {
    console.log('function_2: '+some_data);
    return callback();
}

will result in:

#:~ function_1!
#:~ function_2: value

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