【20180531】Nodejs 循环陷阱与闭包/修复

循环陷阱与闭包

下述是有问题的代码，因为nodejs的执行是异步的

var fs = require('fs');
var files = ['a.txt', 'b.txt', 'c.txt'];
　  
for (var i = 0; i < files.length; i++) {//这里有了变化
　　fs.readFile(files[i], 'utf-8', function (err, contents) {
　　console.log(files[i] + ': ' + contents);
　　  
    });
}

优化修复：

var fs = require('fs');
var files = ['a.txt', 'b.txt', 'c.txt'];
files.forEach(function (filename) {//这里有了变化
　　fs.readFile(filename, 'utf-8', function (err, contents) {
　　console.log(filename + ': ' + contents);
    });
});

复杂一点的逐行读取：

const puppeteer = require('puppeteer');
var readline = require('readline');
var fs = require('fs');
var os = require('os');
var fReadName = './a.txt';
var fRead = fs.createReadStream(fReadName);
fRead.on('end', ()=>{
    console.log('end');
    enableWriteIndex = false;
});
var objReadline = readline.createInterface({
    input: fRead,
    terminal: true
});
var index = 1;
objReadline.on('line', (line)=>{
    (async () => {
    console.log(index, line);
      const browser = await puppeteer.launch();
    const page = await browser.newPage();
    await page.goto(line);
    await page.screenshot({path:index+'qq.png'});
    browser.close();
    await index ++;
}
)();
});
objReadline.on('close', ()=>{
    console.log('readline close...');
});