# [co](https://npm.taobao.org/package/co) 常见使用场景 - fengmk2

# [co](https://npm.taobao.org/package/co) 常见使用场景

### 定时器 Timers

使用 [co-defer](https://github.com/cojs/defer)

```js
var defer = require("co-defer");

defer.setImmediate(function* () {
  console.log("setImmediate");
});

defer.nextTick(function* () {
  console.log("nextTick");
});

var timer1 = defer.setInterval(function* () {
  console.log("setTimeout 100ms");
  clearTimeout(timer1);
}, 100);

var timer2 = defer.setInterval(function* () {
  console.log("setInterval 100ms");
  clearInterval(timer2);
}, 100);
```

## 并发

### 数组形式

```js
co(function* () {
  var rs = yield [get(1), get(2), get(3), get(4)];
  console.log(rs);
  // [1, 2, 3, 4]
})();
```

### 键值对形式

```js
co(function* () {
  var data = yield {
    name: getName(),
    age: getAge(),
  };
  console.log(data);
  // { name: 'fengmk2', age: 18 }
})();
```

### 限制最大并发数

co 默认没有并发数限制, 可以通过 [co-parallel](https://github.com/visionmedia/co-parallel) 来限制并发数

```js
var parallel = require("co-parallel");
var request = require("co-request");
var co = require("co");

var urls = [
  "http://google.com",
  "http://yahoo.com",
  "http://ign.com",
  "http://cloudup.com",
  "http://myspace.com",
  "http://facebook.com",
  "http://segment.io",
];

function* status(url) {
  console.log("GET %s", url);
  return (yield request(url)).statusCode;
}

co(function* () {
  var reqs = urls.map(status);
  var res = yield parallel(reqs, 2);
  console.log(res);
})();
```

### 并发请求容错处理

[co-gather](https://npm.taobao.org/package/co-gather) 并发多个请求, 即使其中有一些请求错误了, 也能容错返回

```js
var gather = require("co-gather");
var wait = require("co-wait");
var co = require("co");

var index = 0;
function* random(val) {
  var i = index++;
  yield wait(Math.random() * 100);
  if (Math.random() > 0.5) {
    throw new Error("error");
  }
  return { index: i, value: val };
}

co(function* () {
  var ret = yield gather([random(1), random(2), random(3), random(4), random(5)]);
  console.log(ret);
})();
```

=>

```js
[
  { isError: false, value: {index: 0, value: 1} },
  { isError: true, error: [Error: error] },
  { isError: true, error: [Error: error] },
  { isError: true, error: [Error: error] },
  { isError: false, value: {index: 4, value: 5} }
]
```

默认并发数为 `concurrency = 5`, 可以自行设置并发数 `gather(thunks, [concurrency])`

### 只取最快响应的

[co-any](https://github.com/cojs/any) 并发多个请求, 返回最快响应的一个结果

```js
var any = require("co-any");
var wait = require("co-wait");
var co = require("co");

function* random(val) {
  yield wait(Math.random() * 100);
  if (Math.random() > 0.5) {
    throw new Error("error");
  }
  return val;
}

co(function* () {
  var ret = yield any([random(1), random(2), random(3), random(4), random(5)]);
  console.log(ret);
})();
```

=>

```js
{
  _key: 1,
  value: 2
}
```

## 事件 EventEmitter

### 事件监听者支持 `GeneratorFunction`

使用 [co-event-wrap](https://npm.taobao.org/package/co-event-wrap)

```js
var co = require("co");
var http = require("http");
var eventWrap = require("co-event-wrap");
var fs = require("co-fs");

co(function* () {
  var req = http.get("http://cnodejs.org");
  eventWrap(req);
  req.on("response", function* (res) {
    res = eventWrap(res);
    var datas = [];
    res.on("data", function* (data) {
      datas.push(data);
    });
    res.on("end", function* () {
      var body = Buffer.concat(datas);
      yield fs.writeFile(__dirname + "/cnodejs.html", body);
      console.log("got %d bytes, headers: %j", body.length, res.headers);
    });
  });
})();
```

### 通过 while 方式处理事件

[co-event](https://npm.taobao.org/package/co-event) 帮你实现

```js
var event = require('co-event');

var e;
while (e = yield event(emitter)) {
  switch (e.type) {
    case 'end':
      break;

    case 'close':
      break;

    case 'error':
      break;
  }
}
```

emitter 原来的事件依旧会触发, 但是 `error` 事件不会被触发, 否则抛错无法被处理.

理解上面代码, 你必须以纯同步的思维来理解.

## 有爱

- 希望本文对你有用 ^\_^
- [原始链接](/blog/2014/07/co-usage.html)