使用pdfjs-dist提取PDF文本报错Promise.withResolvers is not a function

问题详情 #

我编写了一个提取PDF文本的服务，使用pdfjs-dist@4.3.136，无论是导入主构建包还是官方建议的legacy版本，运行时都报错：

TypeError: Promise.withResolvers is not a function
at new PDFDocumentLoadingTask (pdf.mjs:15693:31)
at Module.getDocument (pdf.mjs:15511:1)
at _callee$ (pdfJsService.js:23:23)
at tryCatch (pdfJsService.js:2:1)
at Generator.<anonymous> (pdfJsService.js:2:1)
at Generator.next (pdfJsService.js:2:1)
at asyncGeneratorStep (pdfJsService.js:2:1)
at _next (pdfJsService.js:2:1)
at pdfJsService.js:2:1
at initializePromise (es6-promise.js:437:1)

服务代码：

import * as pdfjsLib from "pdfjs-dist/legacy/build/pdf.mjs";

// Specify the path to the worker script
pdfjsLib.GlobalWorkerOptions.workerSrc = `//cdnjs.cloudflare.com/ajax/libs/pdf.js/4.3.136/pdf.worker.min.js`;

// Function to decode base64 string to Uint8Array
function base64ToUint8Array(base64) {
  const binaryString = atob(base64);
  const len = binaryString.length;
  const bytes = new Uint8Array(len);
  for (let i = 0; i < len; i++) {
    bytes[i] = binaryString.charCodeAt(i);
  }
  return bytes;
}

// Function to extract text from a base64 encoded PDF
export async function extractPdfText(base64String) {
  // Convert base64 string to buffer
  const pdfArray = base64ToUint8Array(base64String);

  try {
    const pdf = await pdfjsLib.getDocument({ data: pdfArray }).promise;
    let extractedText = "";

    for (let i = 1; i <= pdf.numPages; i++) {
      const page = await pdf.getPage(i);
      const textContent = await page.getTextContent();
      const textItems = textContent.items.map((item) => item.str).join(" ");
      extractedText += textItems + "\n";
    }

    console.log("extractedText ________+++++++++++++++++++++++++____________");
    console.log(extractedText);
    return extractedText;
  } catch (error) {
    console.error("Error parsing PDF: ", error);
  }
}

问题原因 #

Promise.withResolvers()是ES2024新增的Promise API，你的运行环境（Node.js版本过低、旧版浏览器）不支持该语法，导致pdfjs-lib v4.x版本的代码执行失败。

解决方案 #

1. 升级运行环境（推荐） #

• Node.js：升级至v21.0.0及以上版本（默认支持Promise.withResolvers）；若使用v20.x版本，需升级到v20.6.0+并添加--experimental-promise-with-resolvers启动标志。
• 浏览器：升级到支持该API的版本，如Chrome 119+、Firefox 120+、Edge 119+等。

2. 降级pdfjs-dist到兼容版本 #

pdfjs-dist从v4.x开始使用Promise.withResolvers，降级到v3.x版本可避免该问题：

npm uninstall pdfjs-dist
npm install pdfjs-dist@3.11.174

同时修改代码中的导入和worker路径：

import * as pdfjsLib from "pdfjs-dist/legacy/build/pdf.mjs";
pdfjsLib.GlobalWorkerOptions.workerSrc = `//cdnjs.cloudflare.com/ajax/libs/pdf.js/3.11.174/pdf.worker.min.js`;

3. 添加Polyfill（适配无法升级环境的场景） #

在导入pdfjs-lib前，手动添加Promise.withResolvers的兼容实现：

// 放在所有导入语句之前
if (!Promise.withResolvers) {
  Promise.withResolvers = function () {
    let resolve, reject;
    const promise = new Promise((res, rej) => {
      resolve = res;
      reject = rej;
    });
    return { promise, resolve, reject };
  };
}

// 之后再导入pdfjs-lib
import * as pdfjsLib from "pdfjs-dist/legacy/build/pdf.mjs";
// ... 其余代码不变

内容的提问来源于stack exchange，提问作者Ryan Durrant