release zalgo: Asynchronous functions may call callback function response data synchronously which would bring inconsistency.
-
The community has provided many solutions for the problems, the winner is Promise, it is built into ECMAScript 2015. On the basis of Promise, and Generator with the ability to switch context, we can write asynchronous code in synchronous way with co and other third party libraries. Meanwhile async function, the official solution has been published in ECMAScript 2017 and landed in Node.js 8.
+
The community has provided many solutions for the problems, the winner is Promise, it is built into ECMAScript 2015. On the basis of Promise, and with the ability of Generator to switch context, we can write asynchronous code in synchronous way with co and other third party libraries. Meanwhile async function, the official solution has been published in ECMAScript 2017 and landed in Node.js 8.
Async function is a syntactic sugar at the language level. In async function, we can use await to wait a promise resolved(or rejected, which will throw an exception), and Node.js LTS (8.x) is support this feature.
+
Async function is a syntactic sugar at the language level. In async function, we can use await to wait for a promise to be resolved(or rejected, which will throw an exception), and Node.js LTS (8.x) has supported this feature.
Koa is a new Web framework designed by the team behind Express, which aims to be a smaller, more expressive, and more robust foundation for Web applications and APIs.
-
The design style of Koa and Express are very similar, The underlying base library is the same, HTTP library. There are several significant differences between them. Besides the asynchronous solution by default metioned above, there are the following points.
+
The design styles of Koa and Express are very similar, The underlying basic library is the same, HTTP library. There are several significant differences between them. Besides the asynchronous solution by default mentioned above, there are the following points.
All the requests will be executed twice during one middleware. Compared to Express middleware, it is very easy to implementing post-processing logic. You can obviously feel the advantage of Koa middleware model comparing to the compress middleware implementing in Koa and Express.
+
All the requests will be executed twice during one middleware. Compared to Express middleware, it is very easy to implement post-processing logic. You can obviously feel the advantage of Koa middleware model by comparing the compress middleware implementing in Koa and Express.
Unlike that there are only two objects Request and Response in Express, Koa has one more, Context object in one HTTP request(it is this in Koa 1, while it is the first parameter for middleware function in Koa 2). We can attach all the relative things to the object. Such as traceId that runs through the request lifetime (which will be called anywhere afterward) could be attached. It is more semantic other than request and response.
-
At the same time Request and Response are attached to Context object. Just like Express, the two objects provide lots of easy ways to help developing. For example:
+
Unlike that there are only two objects Request and Response in Express, Koa has one more, Context object in one HTTP request(it is this in Koa 1, while it is the first parameter for middleware function in Koa 2). We can mount all the related properties in one request to this object. Such as traceId that runs through the whole request lifetime (which will be called anywhere afterward) could be mounted. It is more semantic other than request and response.
+
At the same time Request and Response are mounted to Context object. Just like Express, the two objects provide lots of easy ways to help developing. For example:
Another enormous advantage for writing asynchronous code in synchronous way is that it is quite at ease to handler exception. You can catch all the exceptions thrown in the codes followed the convention with try catch. We can easily write a customized exception handlering middleware.
+
Another enormous advantage for writing asynchronous code in synchronous way is that it is quite at ease to handle exception. You can catch all the exceptions thrown in the codes followed the convention with try catch. We can easily write a customized exception handling middleware.
In the framework or application based on Egg, we can extend the prototype of 4 Koa objects by defining app/extend/{application,context,request,response}.js. With this, we can write more utility methods quickly. For example, we have the following code in app/extend/context.js:
As is known to all, Many middlewares are imported to provide different kind of features in Express and Koa. Eg, koa-session provides the Session support, koa-bodyparser help to parse request body. Egg has provided a powerful plugin mechanism to make it more easy to write stand alone features.
+
As is known to all, Many middlewares are imported to provide different kind of features in Express and Koa. Eg, koa-session provides the Session support, koa-bodyparser help to parse request body. Egg has provided a powerful plugin mechanism to make it easier to write stand alone features.
One plugin can include:
extend：extend the context of base object, provide utility and attributes.
When Egg 1.x released, the Node.js LTS version does not support async function，so Egg 1.x is based on Koa 1.x. On the basis of this, Egg has added full async function support. Egg is completely compatible with middlewares in Koa 2.x, all application could write with async function.
+
When Egg 1.x released, the Node.js LTS version did not support async function，so Egg 1.x was based on Koa 1.x. On the basis of this, Egg had added fully async function support. Egg is completely compatible with middlewares in Koa 2.x, all applications could write with async function.
The underlying is based on Koa 1.x, asynchronous solution is based on generator function wrapped by co.
Official plugin and core of Egg are written in generator function, keep supporting Node.js LTS version, use co when necessary to be compatiable with async function.
Application developers can choose either async function (Node.js 8.x+) or generator function (Node.js 6.x+).
When Node.js 8 became LTS version, async function can used in Node.js without any performance problem. Egg released 2.x based on Koa 2.x, the framework and built-in plugins are all written by async function, and Egg 2.x still keep compatibility with generator function and all the usages in Egg 1.x, applications base on Egg 1.x can migrate to Egg 2.x only by upgrade to Node.js 8.
+
When Node.js 8 became LTS version, async function could be used in Node.js without any performance problem. Egg released 2.x based on Koa 2.x, the framework and built-in plugins were all written by async function, and Egg 2.x still kept compatibility with generator function and all the usages in Egg 1.x, applications based on Egg 1.x can migrate to Egg 2.x only by upgrading to Node.js 8.
The underlying will be based on Koa 2.x, asynchronous solution will be based on async function.
-
Official plugin and core of egge will be written in async function.
-
Recommend user transfer business layer to async function.
+
Official plugin and core of egg will be written in async function.
+
Recommend user to transfer business layer to async function.
This guide covers getting up and running with Egg using a real example.
+
This guide covers getting up and running a real example using Egg.
By following along with this guide step by step, you can quickly get started with Egg development.
Usually you could just use egg-init of the last session,
+
Usually you can just use egg-init of the previous section,
choose a scaffold that best fits your business model and quickly generate a project,
then get started with the development.
However, in this section, instead of using scaffolds we will build a project called Egg HackerNews step by step, for a better understanding of how it works.
In most cases, data are usually read, processed and rendered by the templates before being presented to the user.
Thus we need to introduce corresponding template engines to handle it.
-
Egg does not force the use of any particular template engines,
-but instead specifies the View Plug-ins Specification
-to allow the developers to use different plug-ins for their individual needs.
+
Egg does not force to use any particular template engines,
+but specifies the View Plug-ins Specification
+to allow the developers to use different plug-ins for their individual needs instead.
In practice, controllers usually won't generate data on their own,
neither will they contain complicated business logic.
-Complicated business logic should instead be abstracted as
-a busineess logic layer, i.e., service.
+Complicated business logic should be abstracted as
+a busineess logic layer instead, i.e., service.
Let's create a service to fetch data from the
HackerNews.
// app/service/news.js const Service = require('egg').Service;
We might encounter a small problem here.
-The time that we fetched are in Unix Time,
+The time that we fetched are Unix Time format,
whereas we want to present them in a more friendly way to read.
Egg provides us with a quick way to extend its functionalities.
We just need to add extension scripts to the app/extend directory.
@@ -161,13 +161,13 @@
We can only touch the tip of the iceberg of Egg with the above short sections.
-Where to go from here? Browse our documentation to better understand the framework.
+Where to go from here? read our documentation to better understand the framework.
Egg provides a powerful mechanism for extending features. See Plugin.
-
Egg framework allows small or large teams to work together as fast as possible under the well-documented conventions and coding best practices. In addition, the teams can build up logics on top of the framework to better suited their special needs. See more on [Frameworks].(../advanced/framework.md).
+
Egg framework allows small or large teams to work together as fast as possible under the well-documented conventions and coding best practices. In addition, the teams can build up logics on top of the framework to better suit their special needs. See more on [Frameworks].(../advanced/framework.md).
Egg framework provides code reusabilities and modularities. See details at Progressive.
Egg framework enables developers to write painless unit testing with many plugins and community-powered toolings. The team should give it a try by using Egg unit testing without worrying about setting up the testing tooling but writing the testing logics. See Unit Testing.
