Variable scope & Callback woes - json

Question

This program is reading through the nested object searching for a specific key & values. Once this data is found it has to initiate callback to send back the data. The object looks like this:
{
"name": "joel",
"title": "CTO",
"edu": {
"school": "RMB",
"college": "GNK",
"pg": "CDAC",
"extract": "This is a large text ..."
}
}
Here as I come from synchronous programming background I am not able to understand when I have to initiate the callback and also ensure variables are in scope
function parseData(str, callback) {
function recursiveFunction(obj) {
var keysArray = Object.keys(obj);
for (var i = 0; i < keysArray.length; i++) {
var key = keysArray[i];
var value = obj[key];
if (value === Object(value)) {
recursiveFunction(value);
}
else {
if (key == 'title') {
var title = value;
}
if (key == 'extract') {
var extract = value.replace(/(\r\n|\n|\r)/gm," ");
callback(null, JSON.stringify({title: title, text: extract}));
}
}
}
}
recursiveFunction(str, callback(null, JSON.stringify({title: title, text: extract})));
};
when this code is executed we get following error
/parseData.js:29
recursiveFunction(str, callback(null, JSON.stringify({title: title, text: extract})));
^
ReferenceError: title is not defined

Answer 1

Okay. So you want a function that retrieves the first property named title and the first property named extract from a nested object, no matter how deeply nested these properties are.
"Extract a property value from an object" is basically is a task in its own right, we could write a function for it.
There are three cases to handle:
The argument is not an object - return undefined
The argument contains the key in question - return the associated value
Otherwise, recurse into the object and repeat steps 1 and 2 - return according result
It could look like this:
function pluck(obj, searchKey) {
var val;
if (!obj || typeof obj !== "object") return;
if (obj.hasOwnProperty(searchKey)) return obj[searchKey];
Object.keys(obj).forEach(function (key) {
if (val) return;
val = pluck(obj[key], searchKey);
});
return val;
}
Now we can call pluck() on any object and with any key and it will return to us the first value it finds anywhere in the object.
Now the rest of your task becomes very easy:
var obj = {
"name": "joel",
"title": "CTO",
"edu": {
"school": "RMB",
"college": "GNK",
"pg": "CDAC",
"extract": "This is a large text ..."
}
}
var data = {
title: pluck(obj, "title"),
text: pluck(obj, "extract")
};

Answer 2

This function that you 've posted above has nothing to do with async programming. I will respond in the context of the chunk of code that you 've posted. The error that you have is because you are calling the recursiveFunction(str, callback(null, JSON.stringify({title: title, text: extract}))); but the title variable is nowhere defined. I can see a definition of the title but it is in the the context of the recursiveFunction function. The variables that you define in there are not visible outside of the scope of that function and that's why you have this error.
You are trying to do something strange in this line:
recursiveFunction(str, callback(null, JSON.stringify({title: title, text: extract})));
This line will invoke the callback and will pass in the recursiveFunction the results of this function. I would expect to see something like that in this line:
recursiveFunction(str, callback);