为什么node.js将错误视为回调中的第一个参数

Question

I have the following simple code.. however the "data" variable doesn't return the contents of input.txt.

var fs = require("fs");

fs.readFile('input.txt', function (data) {
     console.log(data.toString());
});

console.log("Program Ended");

The code below works because node.js reads the first parameter, err, and the input.txt contents come from the 2nd parameter

var fs = require("fs");

fs.readFile('input.txt', function (err, data) {
   if (err) return console.error(err);
   console.log(data.toString());
});

console.log("Program Ended");

Is this just a node.js thing to look for the error in the first parameter? What if I did not want to check for an error in the callback function?

Answer 1

It's convention to pass error as the first parameter to a callback function. It's first to prevent it from being ignored. You don't have to check it, of course, but if there is an error it's likely that your data is bad or meaningless anyway.

The reason that fs.readFile('input.txt', function (data) { doesn't work is that the error is passed into your data variable, since it is the first parameter. What you actually name the parameters doesn't matter, the parameter order is decided by fs.readFile .