NETWORK:
style.css

用chrome打开index.html后检查元素就会发现index.html index.js缓存下来了,而style.css没有缓存。

## web workers
1. 什么是Web Worker?
  web worker是运行在后台的Javascript,独立于其他脚本,不会影响页面的性能
2. 方法:
  postMessage()-它用于向HTML页面传回一段消息
  terminate()-终止web worker,并释放浏览器/计算机资源
3. 事件:
  onmessage
#### 代码示例
创建主文件:index.html
```html



    
    
    


    0
    start
    stop

创建:index.js

var numDiv;
var work = null;

window.onload = function(){
    numDiv = document.getElementById("numDiv");

    document.getElementById("start").onclick = startWorker;
    document.getElementById("stop").onclick = function(){
 if(work){
     work.terminate();
     work = null;
 }
    }
}

function startWorker(){
    if(work){
 return;
    }
    work = new Worker("count.js");
    work.onmessage = function(e){
 numDiv.innerHTML = e.data;
    }
}

var countNum = 0;
function count(){
    postMessage(countNum);
    countNum++;
    setTimeout(count,1000);
}

count();