web worker的作用域

Question

<script>
    let worker = new Worker('./work.js')
    worker.addEventListener('message',function(e){
        console.log(e.data)
    })
</script>

work.js:

console.log(this)
self.postMessage({result})

一般的this/self的指向都是window对象
为什么work.js中指向了DedicatedWorkerGlobalScope对象( Worker 全局作用域)