console.log(a)timer(3000,function(x){console.log(x)}) 这种写法函数名都不需要了(术语称为"匿名函数"),在nodejs代码中更为常见也更好理解,翻译成自然语言就是:定时3秒,完成后再回头调用function(x)里面的内容。 nodejs编程中大量使用了异步编程技术,这是为了高效使用硬件,同时也可以不造成同步阻塞。其实nod...
Node.js学习 - CallBack Function Node.js异步编程的直接体现就是回调,Node使用了大量的回调函数,其所有的API都支持回调。 阻塞代码实例(同步) varfs = require("fs");vardata = fs.readFileSync('input.txt'); #读取文件,程序阻塞在这里,等待读取完毕再往下进行 console.log(data.toString()); console.log...
functionpick(next){setTimeout(()=>{console.log('收到信息',newDate());next(); },500); }functiongroundMouth(next){setTimeout(()=>{console.log('货物装载',newDate());next(); },400); }functionblow(next){setTimeout(()=>{console.log('打包出仓',newDate());next(); },300); }fu...
functionmayJunPromisify(original){if(typeoforiginal!=='function'){// {1} 校验thrownewError('The "original" argument must be of type Function. Received type undefined')}functionfn(...args){// {2}returnnewPromise((resolve,reject)=>{try{// original 例如,fs.readFile.call(this, 'filename'...
functionstart(){fs.readFile(f,process);}functionprocess(data){// do somethingwrite(data);}...
a=2,3,4,5 b=45,6,7,8 node:internal/process/promises:265 triggerUncaughtException(err, true /* fromPromise */); ^ [UnhandledPromiseRejection: This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with ...
A tool for making and composing asynchronous promises in JavaScript Q是一个提供制作和创作异步Promise的JavaScript工具。Q 提供了一些辅助函数,可以将Node和其他环境适配为promise可用的。 JavaScript Promise库 Q示例 官网给了一个简单的转换的例子 step1(function (value1) { ...
functionsaveFile(file_name,contents,cb){mkdirp(path.dirname(file_name)).catch(err=>{returncb(err)}).then(p=>{writeFile(file_name,contents,cb)})}exportfunctiondownload(url,file_name,cb){console.log(`downloading${url}`)superagent.get(url).end((err,res)=>{if(err)...
然后修改util.js添加辅助函数: function getLinkUrl(current_url, element) { //抓取的内部链接对应域名要与当前网页域名一样,这样才能保证抓取的是内部链接 const parsedLink = new URL(element.attribs.href || '', current_url) const currentParsedUrl = new URL(current_url) ...
1{printf("Hello, this is Callback_1\n");return0;}intCallback_2()// Callback Function 2{...