从fs.readFileSync（）到fs.readFile（）的Node.js

var fs = require("fs");var filename = "./index.html";function start(resp) {    resp.writeHead(200, {        "Content-Type": "text/html"    });    fs.readFile(filename, "utf8", function(err, data) {        if (err) throw err;        resp.write(data);        resp.end();    });}