如何在node.js中读取多个csv文件

Question

I'm trying to read multiple csv files and then add them as properties to an object, but the async of node.js really prevents me from doing this.

This is the code I tried.

var Converter=require("csvtojson").core.Converter; 
var fs = require('fs');
var csvConverter=new Converter();
var data = {};

for (var i = 0; i < 10; i++)
{   
    var csvFileName="./data/String(i)".csv";

    csvConverter.on("end_parsed",function(jsonObj){
    data['file'+String(i)] = json;


    //read from file
    fs.createReadStream(csvFileName).pipe(csvConverter);
});

}

This leads to a horrible mess, as the for-loop finishes before any of the events are triggered. I would really prefer a synchronous solution to this, but I understand that node.js simply isn't built for that.

So I would be pleased if someone could help me understand how to fix this async. However, this is the first time I've had such a problem. An hour ago I didn't know about the concept asynchronous code.

Answer 1

i is problematic since you can't predict what it is going to be inside the end_parsed callback function, so try:

var fileIndex = 0;
csvConverter.on('end_parsed', function (json) {
    data['file' + fileIndex] = json;
    if (fileIndex === 9) {
       // It is done, call the callback to finish processing
       callback(data);
    }
    fileIndex += 1;
});

var callback = function (data) {
    // Put callback code here
    console.log(data.file0);
};

Really the best way to solve this is to use Promises .