Using AJAX with generators. Demonstrating the exception throwing and handling as well as caching the data.

GeneratorsThrowAndCache.js

// jQuery AJAX simulator

var $ = {
    ajax: function(opts, returnData, throwError) {
        console.log(`Request URL: ${opts.url}`);
        console.log(`Request data: ${opts.data}`);

        var timer = Math.round() * 10 + 1;

        if (throwError && typeof opts.error === 'function') {
            setTimeout(function() {
                opts.error({
                    message: 'AJAX Request Error!'
                });
            }, timer);

            return;
        }

        if (typeof opts.success === 'function') {
            setTimeout(function() {
                opts.success(returnData);
            }, timer);
        }
    }
};

var cache = {};

// Simple wrapper for $.ajax() call

function request(opts, returnData, throwError) {
     if (cache[opts.url]) {
        setTimeout(function() {
            it.next(cache[opts.url]);            
        });
    } else {
        opts.success = function(result) {
            cache[opts.url] = result;
            it.next(result);
        };

        opts.error = function(err) {
            it.throw('Error: ' + err.message);  
        };

        $.ajax(opts, returnData, throwError);
    }
}

// The generator method, which starts the requests

function* main() {
    var res =
        yield request({
            url: 'http://example.com/auth'
        }, {
            id: 24
        });

    try {
        var user =
            yield request({
                url: 'http://example.com/profile',
                data: res.id
            }, {
                name: 'Karlen'
            }, true);

        console.log('User info: ' + JSON.stringify(user));
    } catch (ex) {
        console.log('Error: ' + ex);
    }
}

// Running the generator and starting the first iteration

var it = main();
it.next();