Axios is a simple promise based HTTP client for the browser and node.js. Axios provides a simple to use library in a small package with a very extensible interface.

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Using Javascript on the server side like that requires that you use callbacks. You cannot "return" them like you want, you can however write a function to perform actions on the results.

sequelize.query(query).success(function(row) {
    // Here is where you do your stuff on row
    // End the process
    process.exit();
}

A more practical example, in an express route handler:

// Create a session
app.post("/login", function(req, res) {
    var username = req.body.username,
        password = req.body.password;
    // Obviously, do not inject this directly into the query in the real
    // world ---- VERY BAD.
    return sequelize
      .query("SELECT * FROM users WHERE username = '" + username + "'")
      .success(function(row) {
          // Also - never store passwords in plain text
          if (row.password === password) {
              req.session.user = row;
              return res.json({success: true});
          }
          else {
              return res.json({success: false, incorrect: true});
          }
      });
});

Ignore injection and plain text password example - for brevity.

Functions act as "closures" by storing references to any variable in the scope the function is defined in. In my above example, the correct res value is stored for reference per request by the callback I've supplied to sequelize. The direct benefit of this is that more requests can be handled while the query is running and once it's finished more code will be executed. If this wasn't the case, then your process (assuming Node.js) would wait for that one query to finish block all other requests. This is not desired. The callback style is such that your code can do what it needs and move on, waiting for important or processer heavy pieces to finish up and call a function once complete.

EDIT

The API for handling callbacks has changed since answering this question. Sequelize now returns a Promise from .query so changing .success to .then should be all you need to do.

An AsyncFunction object, representing an asynchronous function which executes the code contained within the function.

Use promises

The Promise API is a new feature of ECMAScript 6, but it has good browser support already. There are also many libraries which implement the standard Promises API and provide additional methods to ease the use and composition of asynchronous functions (e.g. bluebird).

Promises are containers for future values. When the promise receives the value (it is resolved) or when it is cancelled (rejected), it notifies all of its "listeners" who want to access this value.

The advantage over plain callbacks is that they allow you do decouple your code and they are easier to compose.

Here is a simple example of using a promise:

function delay() {
  // `delay` returns a promise
  return new Promise(function(resolve, reject) {
    // Only `delay` is able to resolve or reject the promise
    setTimeout(function() {
      resolve(42); // After 3 seconds, resolve the promise with value 42
    }, 3000);
  });
}

delay().then(function(v) { // `delay` returns a promise
  console.log(v); // Log the value once it is resolved
}).catch(function(v) {
  // Or do something else if it is rejected 
  // (it would not happen in this example, since `reject` is not called).
});

Applied to our Ajax call we could use promises like this:

function ajax(url) {
  return new Promise(function(resolve, reject) {
    var xhr = new XMLHttpRequest();
    xhr.onload = function() {
      resolve(this.responseText);
    };
    xhr.onerror = reject;
    xhr.open('GET', url);
    xhr.send();
  });
}

ajax("/echo/json").then(function(result) {
  // Code depending on result
}).catch(function() {
  // An error occurred
});

Describing all the advantages that promises offer is beyond the scope of this answer, but if you write new code, you should seriously consider them. They provide a great abstraction and separation of your code.

More information about promises: HTML5 rocks - JavaScript Promises