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Accepted
Kevin AB
Asked: 2020-06-03 13:13:48 +0800 CST 2020-06-03 13:13:48 +0800 CST

Why in each iteration does the value of the variable "i" always have the last possible value?

  • 772

How can I generate 20 txt relative to the pages of a pdf?

var fs = require('fs');
var pdfUtil = require('pdf-to-text');
var pdf_path = "/home/kevin/Downloads/principito.pdf";

        var i=0;
        for(i=0;i<=10;i++){
        var option = {from:i, to:i};

var doc='./file'+i+'.txt';
//Omit option to extract all text from the pdf file 
pdfUtil.pdfToText(pdf_path,option, function(err, data) {
     fs.writeFile(doc, data, function(err) {
        if( err ){
            console.log( err );
        }
        else{
            console.log(doc);
        }
    });

});

This is my code, but it generates the following:

./file20.txt
./file20.txt
./file20.txt
./file20.txt
./file20.txt
./file20.txt
./file20.txt
./file20.txt
./file20.txt
./file20.txt
./file20.txt
./file20.txt
./file20.txt
./file20.txt
./file20.txt
./file20.txt
./file20.txt
./file20.txt
./file20.txt
./file20.txt
./file20.txt

everything is concatenated, I guess it's because of the asynchronous behavior of nodejs , a handy.

javascript

1 Answers

  1. Best Answer

    The problem is that you are generating a new function inside your loop every time you call the function pdfToText.

    Each of these functions refer to the same variable i, as the code is not executed immediately by the time it is required to calculate the value of the variable doc, the loop forhas already finished its execution and the value of iis 20

    var doc='./file'+ i +'.txt';  // i = 20

    The result is that all functions write to the same file.

    This is a classic JavaScript problem that can be solved with a IIFE:

    // Encerrar el código con una función
(function (doc) {
    pdfUtil.pdfToText(pdf_path,option, function(err, data) {
        fs.writeFile(doc, data, function(err) {
            if( err ){
                console.log( err );
            }
            else {
                console.log(doc);
            }
        });
    });
})(doc);

    An IIFE is a function that is declared and called immediately, we pass the variable as a parameter docso that a copy is generated, in this way each function will have the correct value of the counter i.

    This concept is also known as closure .

    In ES6 the problem is more easily solved by using the keyword let to declare the variable doc. letallows you to declare variables whose scope is the same block where they were declared.

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