how to correctly extract text from a pdf using pdf

Question

I'm new to ES6 and Promise. I'm trying pdf.js to extract texts from all pages of a pdf file into a string array. And when extraction is done, I want to parse the array somehow. Say pdf file(passed via typedarray correctly) has 4 pages and my code is:

let str = [];
PDFJS.getDocument(typedarray).then(function(pdf) {
  for(let i = 1; i <= pdf.numPages; i++) {
    pdf.getPage(i).then(function(page) {
      page.getTextContent().then(function(textContent) {
        for(let j = 0; j < textContent.items.length; j++) {
          str.push(textContent.items[j].str);
        }
        parse(str);
      });
    });
  }
});

It manages to work, but, of course, the problem is my parse function is called 4 times. I just want to call parse only after all 4-pages-extraction is done. Any advice is welcome. Please shed light on me.

Answer 1

Similar to https://stackoverflow.com/a/40494019/1765767 -- collect page promises using Promise.all and don't forget to chain then's:

function gettext(pdfUrl){
var pdf = PDFJS.getDocument(pdfUrl);
return pdf.then(function(pdf) { // get all pages text
     var maxPages = pdf.pdfInfo.numPages;
     var countPromises = []; // collecting all page promises
     for (var j = 1; j <= maxPages; j++) {
        var page = pdf.getPage(j);

        var txt = "";
        countPromises.push(page.then(function(page) { // add page promise
            var textContent = page.getTextContent();
            return textContent.then(function(text){ // return content promise
                return text.items.map(function (s) { return s.str; }).join(''); // value page text 

            });
        }));
     }
     // Wait for all pages and join text
     return Promise.all(countPromises).then(function (texts) {
       
       return texts.join('');
     });
});
}
// waiting on gettext to finish completion, or error
gettext("https://cdn.mozilla.net/pdfjs/tracemonkey.pdf").then(function (text) {
  alert('parse ' + text);
}, function (reason) {
  console.error(reason);
});

<script src="https://npmcdn.com/pdfjs-dist/build/pdf.js"></script>