how to read specific value from json in an archived file. Using javascript ,and jszip

Question

I am reading a json file from within a zip file using jszip. I can open it and get the information that I want into the console from my function. I can't however get that information out of my javascript function. Maybe I am doing it wrong. Don't usually code using js.

const JSZip = require("jszip");
const fs = require("fs"); 
var myReturn;
function readJsons(bookPath,bookName,fileName,filePath,keyOption){
 


   fs.readFile(bookPath + bookName, function(err, data) {

    if (err) throw err;
    
     JSZip.loadAsync(data).then(function (zip) {
     
      // Read the contents of the '.txt' file
        zip.file(filePath + fileName).async("string").then(function (data) {
        var mydata = JSON.parse(data);
          //gets the value of the key entered
        myReturn = JSON.stringify(mydata[0][keyOption]);       //value here should be "test book"
        console.log(myReturn);                  //printed in console is "test book" works to here
        
          return myReturn;
          
      });
     
     
    });
    
   
    
  });
 
   
}
console.log(readJsons('simplelbook.zip','','frontMatter.json','','bookName'));

Answer 1

The problem is that you are returning inside the callback, so you aren't returning in the actual function. The solution would be using async/await instead:

const JSZip = require("jszip");
const fs = require("fs");
const util = require("util"); // require the util module

const readFile = util.promisify(fs.readFile); // transform fs.readFile into a more compatible form

async function readJsons(bookPath, bookName, fileName, filePath, keyOption) {
  try {
    // this part does the same thing, but with different syntax
    const data = await readFile(bookPath + bookName);
    const zip = await JSZip.loadAsync(data);
    const jsonData = await zip.file(filePath + fileName).async("string");
    const mydata = JSON.parse(jsonData);
    const myReturn = JSON.stringify(mydata[0][keyOption]);

    return myReturn; // return the data, simple as that
  } catch (e) {
    console.error(e); // error handling
  }
}

(async () => { // self executing async function so we can use await
  console.log(
    await readJsons("simplelbook.zip", "", "frontMatter.json", "", "bookName")
  );
})()

Notice I have imported the util module to turn fs.readFile into a function that is more suited for async/await :)