Node.js asynchronous non-blocking callback function

Callback function (asynchronous non-blocking)

main.js file

[code]// 引入文件模块
var fs = require('fs');
// 读取test.txt文件
fs.readFile('test.txt', function (err, data) {
    if (err) return console.log(err);
    console.log(data.toString());
});
console.log('程序执行完毕');

Analysis: execute the program first, then read the file

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