fs 模块的作用是对文件的处理
读
data = fs.readFileSync("./tmp/index.html","utf-8")
写
data = fs.writeFileSync("./tmp/index.html","utf-8")
data = fs.readFile("./tmp/index.html","utf-8",()=>{})
data = fs.writeFile("./tmp/index.html","utf-8",()=>{})