Html5引入Blob对象是要解决什么问题呢，stackoverflow上一位同行说得很好，引文如下：
“Blobs aren't terribly useful on their own. What's useful about them is that they work with many calls which are meant to process Files. The most important of these is URL.createObjectURL(), which can be used to create a URL you can then use in the href or src attributes of HTML tags, @import statements and url() values in CSS, etc.
Basically, Blob gives Javascript something like temporary files, and URL.createObjectURL() lets you treat those blobs as though they were files on a web server.”