nodejs之旅－003－基础知识－全局作用域及全局函数

全局作用域及全局函数

在Nodejs中，一个模块中定义的变量、方法只在该模块中可用，但可以通过exports对象的使用讲起传递到模块外部。但是，仍然存在一个全局作用域，不需要任何模块加载即可使用变量、函数或类。

全局作用域

Nodejs中定义了一个global对象，代表了Nodejs中的全局命名空间，

console.log(global);

{ ArrayBuffer: [Function: ArrayBuffer],  Int8Array: { [Function: Int8Array] BYTES_PER_ELEMENT: 1 },  Uint8Array: { [Function: Uint8Array] BYTES_PER_ELEMENT: 1 },  Uint8ClampedArray: { [Function: Uint8ClampedArray] BYTES_PER_ELEMENT: 1 },  Int16Array: { [Function: Int16Array] BYTES_PER_ELEMENT: 2 },  Uint16Array: { [Function: Uint16Array] BYTES_PER_ELEMENT: 2 },  Int32Array: { [Function: Int32Array] BYTES_PER_ELEMENT: 4 },  Uint32Array: { [Function: Uint32Array] BYTES_PER_ELEMENT: 4 },  Float32Array: { [Function: Float32Array] BYTES_PER_ELEMENT: 4 },  Float64Array: { [Function: Float64Array] BYTES_PER_ELEMENT: 8 },  DataView: [Function: DataView],  DTRACE_NET_SERVER_CONNECTION: [Function],  DTRACE_NET_STREAM_END: [Function],  DTRACE_NET_SOCKET_READ: [Function],  DTRACE_NET_SOCKET_WRITE: [Function],  DTRACE_HTTP_SERVER_REQUEST: [Function],  DTRACE_HTTP_SERVER_RESPONSE: [Function],  DTRACE_HTTP_CLIENT_REQUEST: [Function],  DTRACE_HTTP_CLIENT_RESPONSE: [Function],  global: [Circular],  process:    { title: 'node',     version: 'v0.10.32',     moduleLoadList:       [ 'Binding evals',        'Binding natives',        'NativeModule events',        'NativeModule buffer',        'Binding buffer',        'NativeModule assert',        'NativeModule util',        'NativeModule module',        'NativeModule path',        'NativeModule tty',        'NativeModule net',        'NativeModule stream',        'NativeModule _stream_readable',        'NativeModule _stream_writable',        'NativeModule _stream_duplex',        'NativeModule _stream_transform',        'NativeModule _stream_passthrough',        'NativeModule timers',        'Binding timer_wrap',        'NativeModule _linklist',        'Binding cares_wrap',        'Binding tty_wrap',        'NativeModule vm',        'NativeModule fs',        'Binding fs',        'Binding constants',        'NativeModule readline',        'NativeModule console',        'Binding signal_wrap',        'NativeModule string_decoder' ],     versions:       { http_parser: '1.0',        node: '0.10.32',        v8: '3.14.5.9',        ares: '1.9.0-DEV',        uv: '0.10.28',        zlib: '1.2.3',        modules: '11',        openssl: '1.0.1i' },     arch: 'x64',     platform: 'darwin',     argv: [ 'node' ],     execArgv: [],     env:       { SHELL: '/bin/bash',        TERM: 'xterm-256color',        TMPDIR: '/var/folders/8m/338n1zwx6b54drwph5s0hq780000gn/T/',        Apple_PubSub_Socket_Render: '/private/tmp/com.apple.launchd.u8dfW4kGIc/Render',        OLDPWD: '/Users/wanq/WebstormProjects/NodejsPro',        USER: 'wanq',        SSH_AUTH_SOCK: '/private/tmp/com.apple.launchd.wfqCjimqs6/Listeners',        __CF_USER_TEXT_ENCODING: '0x1F5:0x19:0x34',        PATH: '/Users/wanq/DevTools/mongodb/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin',        PWD: '/Users/wanq/WebstormProjects/NodejsPro/lesson002',        XPC_FLAGS: '0x0',        XPC_SERVICE_NAME: '0',        SHLVL: '1',        HOME: '/Users/wanq',        LOGNAME: 'wanq',        LC_CTYPE: 'zh_CN.UTF-8',        _: '/usr/local/bin/node' },     pid: 9514,     features:       { debug: false,        uv: true,        ipv6: true,        tls_npn: true,        tls_sni: true,        tls: true },     _needImmediateCallback: false,     execPath: '/usr/local/bin/node',     debugPort: 5858,     _getActiveRequests: [Function],     _getActiveHandles: [Function],     _needTickCallback: [Function],     reallyExit: [Function],     abort: [Function],     chdir: [Function],     cwd: [Function],     umask: [Function],     getuid: [Function],     setuid: [Function],     setgid: [Function],     getgid: [Function],     getgroups: [Function],     setgroups: [Function],     initgroups: [Function],     _kill: [Function],     _debugProcess: [Function],     _debugPause: [Function],     _debugEnd: [Function],     hrtime: [Function],     dlopen: [Function],     uptime: [Function],     memoryUsage: [Function],     binding: [Function],     _usingDomains: [Function],     _tickInfoBox: { '0': 1, '1': 0, '2': 0 },     _events: { SIGWINCH: [Function] },     domain: null,     _maxListeners: 10,     EventEmitter: { [Function: EventEmitter] listenerCount: [Function] },     _fatalException: [Function],     _exiting: false,     assert: [Function],     config: { target_defaults: [Object], variables: [Object] },     nextTick: [Function: nextTick],     _currentTickHandler: [Function: _nextTick],     _nextDomainTick: [Function: _nextDomainTick],     _tickCallback: [Function: _tickCallback],     _tickDomainCallback: [Function: _tickDomainCallback],     _tickFromSpinner: [Function: _tickFromSpinner],     maxTickDepth: 1000,     stdout: [Getter],     stderr: [Getter],     stdin: [Getter],     openStdin: [Function],     exit: [Function],     kill: [Function],     addListener: [Function],     on: [Function],     removeListener: [Function] },  GLOBAL: [Circular],  root: [Circular],  Buffer:    { [Function: Buffer]     isEncoding: [Function],     poolSize: 8192,     isBuffer: [Function: isBuffer],     byteLength: [Function],     concat: [Function] },  setTimeout: [Function],  setInterval: [Function],  clearTimeout: [Function],  clearInterval: [Function],  setImmediate: [Function],  clearImmediate: [Function],  console: [Getter],  module:    { id: 'repl',     exports:       { writer: [Object],        _builtinLibs: [Object],        REPLServer: [Object],        start: [Function],        repl: [Object] },     parent: undefined,     filename: '/Users/wanq/WebstormProjects/NodejsPro/lesson002/repl',     loaded: false,     children: [],     paths:       [ '/Users/wanq/WebstormProjects/NodejsPro/lesson002/repl/node_modules',        '/Users/wanq/WebstormProjects/NodejsPro/lesson002/node_modules',        '/Users/wanq/WebstormProjects/NodejsPro/node_modules',        '/Users/wanq/WebstormProjects/node_modules',        '/Users/wanq/node_modules',        '/Users/node_modules',        '/node_modules' ] },  require:    { [Function: require]     resolve: [Function],     main: undefined,     extensions: { '.js': [Function], '.json': [Function], '.node': [Function] },     registerExtension: [Function],     cache: {} } }

setTimeout函数与clearTimeout函数

全局函数setTimeout的作用与客户端javascript中的setTimeout函数的作用类似，延迟多少毫秒执行回调函数。

setTimeout(cb, ms, [arg], [...])

前两个参数是必须输入的，后面的事作为回调函数cb的参数。

//5秒后执行callBackFunvar timer = setTimeout(callBackFun,5000);//取消callBackFun的调用clearTimeout(timer);

setInterval函数与clearInterval函数

全局函数setInterval的作用与客户端javascript的setInterval函数的作用类似，起定时器的作用，每隔多少秒就执行回调函数。

setInterval(cb, ms, [arg], [...]);

同样的前两个参数是必输的，后面的参数作为回调函数的参数。

//每隔5秒执行回调函数callBackFunvar timer = setInterval(callBackFun, 5000);//取消callBackFun的调用clearInterval(timer);

定时器对象的unref方法与ref方法

setTimeout方法与setInterval方法均返回一个定时器对象。定时器对象有unref方法与ref方法。

unref方法是取消调用回调函数。

在调用unref方法后，可以用ref方法恢复定时器调用回调函数。

与模块相关的全局函数及对象

1、使用require函数加载模块

加载模块

var foo = require('../foo.js');var http = require('http');

testModule.js

/** * Created by wanq on 14/11/13. */var testVar = 'This is a variable form testModule.js';exports.testVar = testVar;

app.js

/** * Created by wanq on 14/11/14. */var testModule = require('./testModule.js');console.log(testModule.testVar);

2、使用require.resolve函数查询完整模块名

require.resolve('./testModule.js');//得到testModule.js的目录及文件名

3、require cache对象

require.cache对象代表了缓存了所有已被加载模块的缓存区