Elegant asynchronous control flow with IcedCoffeeScript

Writing Node.js code to interact with external services (databases, email, http, etc.) can easily turn into a cumbersome "callback hell".

While there are a number of async control modules out there, such as the excellent async, most of them might be a bit overkill for the most common usage patterns.

However, if you're not a JavaScript purist and you care for code readability and development speed, IcedCoffeeScript can spare you an incredible amount of trouble.

[画像:Asynchronous flow in IcedCoffeeScript]

Here's just a quick real-world example - the code comes from LeasingSH.ro, a project built entirely in Node.js:

method: 'get'
route: ///
 -
 (
 [A-Z]
 [A-Z|\d]{2}
 \d{5}
 )
 \.html$
///

callback: (req, res, next) ->
 [ uid ] = req.params
 query = Product.findOne uid: uid

 if req.isAuthenticated() and req.user.isSalesman
 query.populate
 path: 'dealer'
 select: 'name phone email address'

 await query.lean().exec defer err, product; return next err if err or not product?

 categoryKey = product.category.key

 errors = {}
 await
 helpers.loadSpecialProducts categoryKey, 10, defer errors.specialProducts, specialProducts

 Product.find()
 .select('uid make model price year').slice('pictures', 1)
 .where('isActive').equals(yes)
 .where('isSold').equals(no)
 .where('category.key').equals(categoryKey)
 .limit(5)
 .lean().exec defer errors.suggestedProducts, suggestedProducts

 for own operation, err of errors
 return next err if err

 res.render 'public/product', {
 pageType: 'product'
 product
 specialProducts, suggestedProducts
 }

After waiting to read the product information, we're executing two parallel queries to read additional information (special & suggested products).

It really can't get any easier than this...

The beauty of combining Node.js with IcedCoffeeScript is that you're really getting the best of two worlds:

• The speed and ability to handle concurrent connections characteristic to Node.js - due to its event-based nature, the server can process something else (i.e. another incoming request) while waiting for a background operation to complete;
• The readability and concision of CoffeeScript (similar to Ruby's), enhanced even more by IcedCoffeeScript's elegant way of dealing with callbacks.

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