learnyounode-Lesson-4

上一节课主要讲了在 node 中处理同步的 I/O;在 node 中大部分还是异步的情况。

课程内容:

• fs.readFile()
• readFile 中使用 callbacks 来处理异步的 I/O https://github.com/maxogden/art-of-node#callbacks

课程目标:

Write a program that uses a single asynchronous filesystem operation to
read a file and print the number of newlines it contains to the console
(stdout)

My Solution:

const fs = require("fs");
const file = process.argv[2];

fs.readFile(file, "utf8", (err, buf) => {
  if (err) {
    return console.err(err);
  }
  const result = buf.toString().split("\n").length - 1;
  console.log(result);
});

Officical Solution:

var fs = require("fs");
var file = process.argv[2];

fs.readFile(file, function(err, contents) {
  // fs.readFile(file, 'utf8', callback) can also be used
  var lines = contents.toString().split("\n").length - 1;
  console.log(lines);
});

课程总结

fs.readFile(path[,options],callback)异步 I/O（和fs.readFileSync()相对应）

• path <string> | <Buffer> | <URL> | <integer> filename or file descriptor
• options <Object> | <string>
  • encoding <string> | <null> Default: null
  • flag <string> Default: ‘r’
• callback <Function>
  • err <Error>
  • data <string> | <Buffer>