nodejs复习01

console

格式化

console.log("%s:%s", "a", "b") //字符串
console.log("%d.%d", 10.2, 0.12) //整型
console.log("%j", {a: "aa", b: "bb"}) //json

冲定向错误输出柳

• 对于throw Erro, console.error, console.warn
• node exec.js 2 > error.log

查看对象属性和方法

console.dir(obj)
//等价
var util = require('util')
console.log(util.inspect(obj));

计时器

console.time(label)  //开始
console.timeEnd(label)  //结束

查看当前调用栈

//打印当前位置的栈，并跟踪到标准错误输出流
console.trace(label)

断言

console.assert(expression, error message)
//相当于
var assert = require('assert')
assert.okt(expression, error message)

readline

命令行输入数据

var readline = require('readline')
var read = readline.createInterface({
	input: process.stdin,
	output: process.stdout
})
read.question("you name?", function(answer) {
	console.log(answer);
	read.close()
})

向控制台输出组合控制键

//3s后模拟ctrl+u
var readline = require('readline')
var read = readline.createInterface({
	input: process.stdin,
	output: process.stdout
})
read.write("Delete me! Wait for 3 seconds...")
var timer = setTimeout(function () {
	read.write(null, {ctrl: true, name: 'u'})
}, 3000)
//read,write(data, key) key是一个代表键序列的对象

模拟控制台界面

//read.prompt(boolean)  为true或空时可以阻止命令提示符的光标被重置为0
var readline = require('readline')
var read = readline.createInterface({
	input: process.stdin,
	output: process.stdout
})
read.setPrompt('NodeJs>')
read.prompt()
read.on("line", function (line) {
	switch(line.trim()) {
		case 'book1':
			console.log(100);
 			break;
 		case 'book2':
 			console.log(200);
 			break;
 		default:
 			console.log('no');
 			break;
	}
	read.prompt()
})
	.on('close', function () {
		console.log('bye');
		process.exit(0);
	})

module

node_modules文件加载

• module.paths: 数组返回加载的依次路径

module.exports 对象和exports对象

module.parent 指向该module被require时的module，可以用于测试判读

• module.exports是module模块的真正接口， exports是指向它的变量;
• 所以设置module.exports后exports设置就失效了

Buffer

js语言本身仅仅支持Unicode字符串数据处理

初始化

var buffer1 = new Buffer([0x6e, 0x6f, 0x64, 0x65, 0x6a, 0x73])
var buffer2 = new Buffer('nodejs')
//显示都为<Buffer 6e 6f 64 65 6a 73>, 16进制, hex
buffer.toString(encoding, start, end)  // 默认utf8, 还有hex, binary, base64, utf16le, ascii
//特别定义
var buffer = new Buffer(length)     /分配大小为length的8位字节
buffer.write(string, offset, length, encoding)  
//判断是否为指定编码
buffer.isEncoding(encoding)

Buffer字节长度

str.length //字符长度
Buffer.byteLength(str, encoding)  //字节长度

• 在改写http响应头Content-Length时一定要使用该方法而不是修改length

基本操作

var buf = new Buffer('nodejs')
//裁减, buf.slice(start, end)
var buf1 = buf.slice() // 副本, buf1和buf2指向同一地址
buf1[0] = 97  //ASCII 'a'
console.log(buf.toString());  //anodejs
console.log(buf1.toString());  //anodejs
//拷贝 buf.copy(target, targetStart, sourceStart, sourceEnd)
var buf2 = new Buffer(buf.length)
buf.copy(buf2,0,0,buf.length)
buf2[0] = 110  //ASCII 'n'
console.log(buf.toString());  //anodejs
console.log(buf2.toString());  //nnodejs
//拼接  Buffer.concat(list, totalLength)
//如果totalLength没有提供会增加额外的计算
var list = [], len = 0;
for (var i = 0; i < 4; i++) {
	list.push(buf)
	len += buf.length
}
var buf3 = Buffer.concat(list, len)
console.log(buf3.toString());