Table of Contents
1 全局对象
- global
console.log(global); // Object [global] { // global: [Circular], // clearInterval: [Function: clearInterval], // clearTimeout: [Function: clearTimeout], // setInterval: [Function: setInterval], // setTimeout: [Function: setTimeout] { [Symbol(util.promisify.custom)]: [Function] }, // queueMicrotask: [Function: queueMicrotask], // clearImmediate: [Function: clearImmediate], // setImmediate: [Function: setImmediate] { // [Symbol(util.promisify.custom)]: [Function] // } // }
- console
console.log(console) // { // log: [Function: bound consoleCall], // warn: [Function: bound consoleCall], // dir: [Function: bound consoleCall], // time: [Function: bound consoleCall], // timeEnd: [Function: bound consoleCall], // timeLog: [Function: bound consoleCall], // trace: [Function: bound consoleCall], // assert: [Function: bound consoleCall], // clear: [Function: bound consoleCall], // count: [Function: bound consoleCall], // countReset: [Function: bound consoleCall], // group: [Function: bound consoleCall], // groupEnd: [Function: bound consoleCall], // table: [Function: bound consoleCall], // debug: [Function: bound consoleCall], // info: [Function: bound consoleCall], // dirxml: [Function: bound consoleCall], // error: [Function: bound consoleCall], // groupCollapsed: [Function: bound consoleCall], // Console: [Function: Console], // profile: [Function: profile], // profileEnd: [Function: profileEnd], // timeStamp: [Function: timeStamp], // context: [Function: context], // [Symbol(kBindStreamsEager)]: [Function: bound ], // [Symbol(kBindStreamsLazy)]: [Function: bound ], // [Symbol(kBindProperties)]: [Function: bound ], // [Symbol(kWriteToConsole)]: [Function: bound ], // [Symbol(kGetInspectOptions)]: [Function: bound ], // [Symbol(kFormatForStdout)]: [Function: bound ], // [Symbol(kFormatForStderr)]: [Function: bound ] // }
- exports, require, module, _filename, _dirname（模块参数）
console.log(arguments.callee + ''); // function (exports, require, module, __filename, __dirname) { // console.log(arguments.callee + '');
2 代码执行优先级
同步代码优先，例子以下css
// 代码执行优先级 setTimeout(function () { setTimeout(function () { console.log('time out'); }, 0); new Promise(resolve => { setTimeout(function () { console.log('start in Promise'); }, 1); console.log('beg'); resolve(); console.log('end'); setTimeout(function () { console.log('end in Promise'); }, 0); }).then(() => { console.log('finish'); }); console.log('不要调皮'); }, 100); // beg // end // 不要调皮 // finish // time out // start in Promise // end in Promise
3 模块导入
同步导入，module.exports = exports ==> truehtml
{ test } » tree
.
├── index.js
└── test.js
- ./index.js
console.log("index.js");
- ./test.js
require('./index.js'); console.log('test.js');
output: 导入以后才会继续执行代码java
index.js test.js
4 模块加载
4.1 文件模块优先级
这里只考虑 .js .json文件路径加载node
- 文件结构
. ├── a.js ├── a.json ├── b.json └── test.js
- a.js
module.exports = "js文件优先";
- a.json
{
"s": "json文件优先"
}
- b.json
{
"main" : "json 文件也支持省略扩展名的方式加载"
}
- test.js
// 测试js文件先加载 console.log(require('./a')); // 证实json也能够加载 console.log(require('./b'));
- output
- 默认文件加载js先于json文件
js文件优先
{ main: 'json 文件也支持省略扩展名的方式加载' }
4.2 文件夹加载优先级
4.2.1 包（文件夹）下的入口文件优先级
- 文件结构
. ├── a │ ├── index.js │ ├── m.js │ └── package.json ├── b │ ├── index.js │ └── package.json ├── c │ └── index.js └── test.js
- ./a
- index.js
module.exports = "index.js文件优先";- m.js
module.exports = "package.json文件优先";- package.json
{ "name": "a", "version": "1.0.0", "main" : "m.js" } - ./b
- index.js
module.exports = "./b/index.js文件优先";- package.json
{ "name": "a", "version": "1.0.0" } - ./c
- index.js
module.exports = "index.js支持默认加载"; - ./test.js
// 优先加载packagae.json文件 console.log(require('./a')); // packagae.json中main属性指定加载某文件 console.log(require('./b')); // index.js也支持默认加载 console.log(require('./c'));
- output
package.json文件中有main优先于index.js文件 python
package.json文件优先 ./b/index.js文件优先 index.js支持默认加载
4.2.2 包加载优先级
- 路径加载
- 文件结构
. ├── fs │ └── index.js └── test.js
- ./fs/index.js
module.exports = "路径加载优先级高";- ./fs/test.js
// 加载核心模块 console.log(require('fs')); // 第三方模块 console.log(require('./fs'));
- output
路径加载优先级高于核心模块sql
{ appendFile: [Function: appendFile], appendFileSync: [Function: appendFileSync], access: [Function: access], accessSync: [Function: accessSync], chown: [Function: chown], promises: [Getter] ..........//还有不少 } 路径加载优先级高 - 非路径加载
- 文件结构
. ├── node_modules │ ├── fs │ │ └── index.js │ └── tts │ └── index.js └── test.js
- ./node nodules./fs/index.js
module.exports = "./node_nodules./fs";- ./node nodules./tts/index.js
module.exports = "./node_nodules./tts";- ./test.js
// 判断第三方模块和核心模块的优先级 console.log(require('fs')); // 第三方模块能够加载 console.log(require('tts'));
- output
- 核心模块加载优先于第三方模块(node modules)
{ appendFile: [Function: appendFile], appendFileSync: [Function: appendFileSync], access: [Function: access], ......//不少 promises: [Getter] } ./node_nodules./tts - 第三方模块查找过程（非路径查找）
- 文件结构
. ├── a │ ├── b │ │ ├── c │ │ │ ├── node_modules │ │ │ │ └── tts1 │ │ │ │ └── index.js │ │ │ └── t.js │ │ └── node_modules │ │ └── tts2 │ │ └── index.js │ └── node_modules │ └── tts3 │ └── index.js └── node_modules └── tts4 └── index.js- module.paths 中列表的顺序查找
- 递归向上级目录查找
[ 'C:\\a\\b\\c\\node_modules', 'C:\\a\\b\\node_modules', 'C:\\a\\node_modules', 'C:\\node_modules' ]
5 核心模块的简单使用
5.1 events
继承了事件类，自身不用实现事件类shell
const events = require('events'); class Teacher extends events { constructor(sec = 2000) { super(); this.sec = sec; this.doing(); } doing() { let cnt = 0; setInterval(() => { ++cnt; this.emit('class', {cnt}); }, this.sec); } } const t = new Teacher(); t.on('class', function (args) { console.log('time to class:', args.cnt); });