CODEWITHSUNDEEP
javascriptjsonnode.js
jeromekjerome
jeromekjerome

Reputation: 501

passing variables through callback functions in node.js

I posted this question yesterday but I guess I just confused everyone. I got responses like "what exactly is your question?" So I am expanding and reposting today.

The following node.js snippet is from the file "accounts.js" which is in an ETrade api library that exists in the path /lib. It should return json containing data about the accounts of the authenticated user. The authentication part is working great. I'm confused about what exactly is being done in the last line of this function:

this._run(actionDescriptor,{},successCallback,errorCallback);

Ten years ago (the last time I was coding), we didn't have the construct "this" and I haven't a clue about "_run" and Google searches have not been helpful. Here is the function.

exports.listAccounts = function(successCallback, errorCallback) {
  var actionDescriptor = {
    method: "GET",
    module: "accounts",
    action: "accountlist",
    useJSON: true,
  };

  this._run(actionDescriptor, {}, successCallback, errorCallback);
};

I understand that the function is accessed with "et.listAccounts ...." but then my understanding goes all to hell. It's pretty obvious that a get is being executed and json data returned. It's also obvious that the result is passed back through the successCallback.

In my app.js file, I have the following:

var etrade = require('./lib/etrade');
var et = new etrade(configuration);

Can someone please suggest a snippet to be used in app.js that will output the accounts data to the console?

It seems like the json data must be passed back through the successCallback but I'm lost on how to access it on the app.js side.

Suppose in app.js I want to put the accounts data in a variable called myAccounts. The exports.listAccounts function does not specify a return value, so I doubt I can do var myAccounts = et.listAccounts(). Likewise, myAccounts will be undefined if I try to do this: et.listAccounts(){myAccounts, error}. Finally, the listAccounts function contains two possible variable names I could use, "accounts" and "accountlist" but these turn out to be undefined at app.js.

When I put a function in successCallback in app.js to write a generic message to the console, the message appears in the log so I know I am making it into the listAccounts function and back successfully. In this case, the log also shows "Request: [GET]: https://etwssandbox.etrade.com/accounts/sandbox/rest/accountlist.json"

From this I deduce that the data is actually being returned and is available at that end point.

Upvotes: 0

Views: 149

Answers (1)

Jack
Jack

Reputation: 804

Ten years ago (the last time I was coding), we didn't have the construct "this" and I haven't a clue about "_run"

this refers to the current object, further reading here. _run is just what they chose to call the function.

I have no experience with this module, but with a cursory glance at the git repo I suspect you will want to expand your app.js like so: 

et.listAccounts(function(response) {
  console.log(response);
});

In javascript functions are first order and so can be passed around like variables see here. listAccounts wants a function passed to it, and when it is complete it will call it with one parameters, as can be seen in etrade.js.

There is also the function errorCallback which is much the same but is called on an error. You could expand the above snippet like so: 

et.listAccounts(function(response) {
  console.log(response);
}, function(error) {
  console.log(error);
});

Upvotes: 1

Related Questions