NodeJS HTML-pdf：fs.readfilesync如何异步/等待

Question

I have a problem with my html-pdf document creation. The problem is that often the code runs to fast to complete the process of pdf-docutment creation. The Processes consists out of building an HTML-String by replacing placeholders in an Html file. Below you see the code what happens afterwards.

                            Object.keys(setter).forEach(function(element, key, _array) {
                              var regex = new RegExp(element, "g");

                              data = data.replace(regex, setter[element])
                            })

                            var result = data;

                            fs.writeFile(mergeFileRes, result, 'utf8', function (err) {
                                if(err) { 
                                    console.log(err); 
                                    return;
                                } else {

                                    let html2 = fs.readFileSync(mergeFileRes, 'utf8');
                                    let options = { 
                                        format: 'a4' , 
                                        "directory" : "/tmp",
                                    };                            

                                    if(html2){
                                        pdf.create(html2, options).toStream(function(err, stream2){
                                            if(err)  console.log(err);
                                            stream2.pipe(res);

                                            stream2.on('end', function () {
                                                try{
                                                    fs.unlink(mergeFileRes)
                                                    console.log(3090, "deleted file");
                                                }
                                                catch (err){
                                                    console.log(3090, "Did not delete file");
                                                }
                                            });
                                        });
                                    } else {

                                    }
                                }
                            });

My problem is that in many cases the html2 variable is not yet created before the pdf.create process starts. This is probably because the readFileSync takes too long to finish.

I was wondering, how can I fix this. How can I make the pdf.create wait for the readFileSync to finish and the html2 variable to be filled.

Answer 1

You can use fs.readFile to read the file asynchronously and html2 will be available within the callback function.

Object.keys(setter).forEach(function(element, key, _array) {
    var regex = new RegExp(element, "g");

    data = data.replace(regex, setter[element])
})

var result = data;

fs.writeFile(mergeFileRes, result, 'utf8', function (err) {
    if(err) { 
        console.log(err); 
        return;
    } else {

        fs.readFile(mergeFileRes, 'utf8', function(err, html2){
            if (err) throw err;

            let options = { 
                format: 'a4' , 
                "directory" : "/tmp",
            };                            

            pdf.create(html2, options).toStream(function(err, stream2){
                if(err)  console.log(err);
                stream2.pipe(res);

                stream2.on('end', function () {
                    try{
                        fs.unlink(mergeFileRes)
                        console.log(3090, "deleted file");
                    }
                    catch (err){
                        console.log(3090, "Did not delete file");
                    }
                });
            });
        });
    }
});