Beads

Beads is a Koa like, general purpose middleware layer for nodejs.

Usage

``javascript
app.when(function *() {
return isReady;
}).use(function *(next) {
// do sth
yield next;
// do sth later
});
`

`javascript
// will be fired as soon as possible
app.use(function *(next) {
// do sth
yield next;
// do sth later
});
`

`javascript
// add wrap for middleware (adding logger, and log BEGIN and END)
var wrap = function(middleware) {
return function *(_next) {
this.logger = require("log4js").getLogger('YOUR MIDDLEWARE NAME');
this.logger.debug('BEGIN');
var next = function *() {
yield _next;
this.logger = require("log4js").getLogger('YOUR MIDDLEWARE NAME');
}
yield middleware.call(this, next);
this.logger.debug('END');
};
};
app.wrap(wrap).when(function *() {
return isReady;
}).use(function *(next) {
// do sth
yield next;
// do sth later
});
`

Features

- Simple dependency resolution system

Use app.when. See the example below.

Dependency Test -> Functions whose dependency was satisfied -> RUN those functions one by one -> Dependency Test

- Shared context among middlewares

- Use co and generators for middlewares

Example

`javascript
var context = {};
var app = new (require("../index.js"))(context);

app.use(function *(next) {
console.log("set mark1!");
this.mark1 = true;
yield next;
});

app.when(function *() {
return this.mark1;
}).use(function *(next) {
console.log("mark1 set, set mark2!");
this.mark2 = true;
yield next;
});

app.when(function *() {
return this.mark2;
}).use(function *(next) {
console.log("mark2 set!");
yield next;
});

app.when(function *() {
return this.mark1;
}).use(function *(next) {
console.log("mark1 set!");
yield next;
});

app.use(function *(next){
var start = new Date;
console.log("timer start");
yield next;
var t = new Date - start;
console.log("timer end");
console.log(t + "ms");
});

app.run(function(err, context) {
console.log("Output Context: " + JSON.stringify(context));
});
`

The output:
`
set mark1!
timer start
mark1 set, set mark2!
mark1 set!
mark2 set!
Output Context: {"mark1":true,"mark2":true}
timer end
2ms
`

Installation

`
$ npm install beads
`

Compatibility

You can use the --harmony` flag when using node 0.11+.

Or, you can use gnode if you are using node 0.10 or below.

FAQ

$3

Because sometimes you may want to add wrapper for some middleware, add logger or profile. So it's useful to have app.wrap.

$3

You can't use yield inside a regular function!

http://stackoverflow.com/questions/20834113/syntaxerror-unexpected-identifier-generators-in-es6

$3

每次依赖条件已解决，执行一批插件。
插件 A, B 依赖于条件1，插件 C, D 依赖于条件2。
B中会解决条件2。
那么A, B的顺序不确定，但是A, B都先于C, D执行。

如果不是成批执行，
若定义顺序为 B C D A 则实际运行顺序为
B C D A，A的条件本早已满足，却在最后被执行了。

为此依赖必须单独与函数体存在。
否则在执行函数前无法知道依赖是否满足，
但是执行函数可能改变依赖条件，
这样就无法实现无损的依赖判断。