解决 Node.js 代码中 'contentType' 未定义的错误

在代码中没有定义变量 'contentType'，导致在第 64 行调用 'response.setHeader('content-type', contentType);' 时报错。需要在代码中定义 'contentType' 变量并赋值。例如，可以在代码开头添加以下行定义 'contentType' 变量：

const contentType = 'image/png';

完整代码示例：

const fs = require('fs');
const path = require('path');
const puppeteer = require('puppeteer');

const contentType = 'image/png'; // 定义 contentType 变量

const launchBrowser = async () => {
  const browser = await puppeteer.launch({
    args: [
      '--disable-gpu',
      '--disable-dev-shm-usage',
      '--disable-setuid-sandbox',
      '--no-first-run',
      '--no-zygote',
      '--no-sandbox'
    ],
    headless: true,
  });

  return browser;
};

const autoScroll = async (page) => {
  return page.evaluate(() => {
    return new Promise((resolve, reject) => {
      var totalHeight = 0;
      var distance = 100;
      var timer = setInterval(() => {
        var scrollHeight = document.body.scrollHeight;
        window.scrollBy(0, distance);
        totalHeight += distance;
        if (totalHeight >= scrollHeight) {
          clearInterval(timer);
          resolve();
        }
      }, 100);
    });
  });
};

module.exports.handler = async (event, response,  context) => {
  const input = JSON.parse(event.body).input;
  console.log('Input:', input);

  const fileinput = `${Date.now()}.mmd`;
  fs.writeFileSync(`/tmp/${fileinput}`, input);

  const output = `${Date.now()}.png`;
  const browser = await launchBrowser();
  const page = await browser.newPage();
  await page.emulateTimezone('Asia/Shanghai');

  try {
    const html = fs.readFileSync(path.join(__dirname, 'template.html'), 'utf8');
    const renderedHtml = html.replace('{{mermaid}}', input);
    const filehtml = `${Date.now()}.html`;
    fs.writeFileSync(`/tmp/${filehtml}`, renderedHtml);
    let url = 'file://' + path.join('/tmp', filehtml);
    await page.goto(url, { waitUntil: 'networkidle2' });
    await page.setViewport({ width: 1200, height: 800 });
    await autoScroll(page);
    await page.screenshot({ path: `/tmp/${output}`, fullPage: true, type: 'png' });

    console.log('Image generated:', output);
    const imageStream = fs.createReadStream(`/tmp/${output}`);
    response.setHeader('content-type', contentType); // 使用定义的 contentType 变量
    response.send(imageStream);
  } catch (err) {
    console.error(err);
  } finally {
    await browser.close();
  }
};

通过在代码开头定义 'contentType' 变量并赋值为 'image/png'，就可以解决 'contentType' 未定义的错误。