NodeJS Read file, make node-rest-client call to get related data and add retrieved response as element in JSON - node.js

Question

I am reading JSON file using fs.readFileSync and for each document obtained, I am making a rest API call using client.post. Once I get response, I want to place the received content into another JSON file which is a replica of input JSON except additional element which is the data received from client.post call. However probably because of async nature of client.post, I am unable to add element to output JSON. I am new to NodeJS. Can you please help me where I am missing. Below is code and data
data:
[
{
"ticker": "CLYD"
},
{
"ticker": "EGH"
}
]
Code:
var fs = require('fs');
var Client = require('node-rest-client').Client;
var data = fs.readFileSync(__dirname + "/data/stocks.json", "utf8");
processData(data);
function processData (data) {
var obj = JSON.parse(data);
for (j = 0; j < obj.length; j++) {
obj[j].stockInformation = getValuesForTicker (obj[j].ticker.trim());
}
var jsonOutput = JSON.stringify(obj,null,'\t');
fs.writeFileSync(__dirname + "/data/response.json", jsonOutput);
};
function getValuesForTicker (ticker) {
/**
* More details and samples at https://www.npmjs.com/package/node-rest-client
*/
var client = new Client();
var values;
// set content-type header and data as json in args parameter
var args = {
data: { "ticker" : ticker},
headers: { "Content-Type": "application/json", "Accept" : "application/json" }
};
var responseToRequest = client.post("https://url.providing.response.as.json.content/", args, function (data, response) {
// parsed response body as js object
values = JSON.parse(JSON.stringify(data)).price;
});
return values;
};

Answer 1

Since getValueForTicker makes a async call to fetch data it should call a callback once data is recieved (or better a promise) and not return the result (currently undefined is returned as the value is returned before the value is assigned)
function getValuesForTicker (ticker, callback) {
/**
* More details and samples at https://www.npmjs.com/package/node-rest-client
*/
return new Promise(function(resolve, reject) {
var client = new Client();
var values;
// set content-type header and data as json in args parameter
var args = {
data: { "ticker" : ticker},
headers: { "Content-Type": "application/json", "Accept" : "application/json" }
};
var responseToRequest =
client.post("https://url.providing.response.as.json.content/", args, function (data, response) {
// parsed response body as js object
values = JSON.parse(JSON.stringify(data)).price;
resolve(values)
});
};
})
and to get the data once async call is done you will need to call then function as below:
getValuesForTicker(obj[j].ticker.trim())
.then(function(val) {
obj[j].stockInformation = val
})
Considering you are new to node.js it will be hard to get.Take some time to understand callback and promise first.