How to correctly extract text from a pdf using pdf.js

问题

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.

回答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>

回答2:

A bit more cleaner version of @async5 and updated according to the latest version of "pdfjs-dist": "^2.0.943"


import PDFJS from "pdfjs-dist";

PDFJS.disableTextLayer = true;
PDFJS.disableWorker = true;

const getPageText = async (pdf: Pdf, pageNo: number) => {
  const page = await pdf.getPage(pageNo);
  const tokenizedText = await page.getTextContent();
  const pageText = tokenizedText.items.map(token => token.str).join("");
  return pageText;
};

export const getPDFText = async (source: PDFSource): Promise<string> => {
  const pdf: Pdf = await PDFJS.getDocument(source).promise;
  const maxPages = pdf.numPages;
  const pageTextPromises = [];
  for (let pageNo = 1; pageNo <= maxPages; pageNo += 1) {
    pageTextPromises.push(getPageText(pdf, pageNo));
  }
  const pageTexts = await Promise.all(pageTextPromises);
  return pageTexts.join(" ");
};

This is the corresponding typescript declaration file that I have used if anyone needs it.

declare module "pdfjs-dist";

type TokenText = {
  str: string;
};
type PageText = {
  items: TokenText[];
};
type PdfPage = {
  getTextContent: () => Promise<PageText>;
};
type Pdf = {
  numPages: number;
  getPage: (pageNo: number) => Promise<PdfPage>;
};

type PDFSource = Buffer | string;

来源：https://stackoverflow.com/questions/40635979/how-to-correctly-extract-text-from-a-pdf-using-pdf-js

标签

javascript

pdf

callback

es6-promise

pdf.js