异步处理

回调函数处理异步

const mime = require("./model/mime");

function getMime(cb) {
  fs.readFile("./json/mime.json", (err, data) => {
    if (err) throw err;
    cb(JSON.parse(data.toString()));
  });
}

getMime(val => {
  console.log(val);
});

events 模块处理异步

• 基础模样

const events = require("events");

const EventEmitter = new events.EventEmitter();

EventEmitter.on("to_parent", data => {
  console.log("接收到了这个广播事件");
  console.log(data);
});

setTimeout(() => {
  console.log("开始广播");
  EventEmitter.emit("to_parent", "发送的数据");
}, 2000);

• 实例

exports.getType = (fs, EventEmitter, extname) => {
  fs.readFile("./json/mime.json", (err, data) => {
    if (err) throw err;
    mimeType = JSON.parse(data.toString())[extname];
    EventEmitter.emit("mime_type", mimeType);
  });
};