Stuck on an issue?

Lightrun Answers was designed to reduce the constant googling that comes with debugging 3rd party libraries. It collects links to all the places you might be looking at while hunting down a tough bug.

And, if you’re still stuck at the end, we’re happy to hop on a call to see how we can help out.

async function inside evaluate fails

See original GitHub issue

Code

await page.evaluate(async () => {
    console.log('1')
})

Error

(node:66796) UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 1): Error: Evaluation failed: ReferenceError: fn is not defined
    at <anonymous>:1:26

Issue Analytics

State:
Created 6 years ago
Reactions:15
Comments:16 (6 by maintainers)

Top GitHub Comments

88reactions

JoelEinbindercommented, Dec 28, 2017

Are you transforming your code with babel? The babel async function code isn’t compatible with Puppeteer. We call function.toString and send your code into Chromium, but babel messes with that and we end up sending an incomplete string. You can get around this by using template strings instead of functions.

await page.evaluate(`(async() => {
   console.log('1');
})()`);

63reactions

cancerberoSgxcommented, Oct 12, 2018

same issue, different error, using TypeScript (not babel). The solution for me was to instruct TypeScript to compile to latest ecma version so no pollyfills / artificial code is generated for async function support, in tsconfig.json file:

{
  "compilerOptions": {
    "target": "es2018"
  }
}

issue details

While the following works OK:

    let result = await page.evaluate( ()=>{
      return Promise.resolve('hello')
    })

the equivalent code using async functions throws the following error:

    let result = await page.evaluate(async ()=>{
      return 'hello'
    })

Error:

  Message:
    Error: Evaluation failed: ReferenceError: __awaiter is not defined
        at __puppeteer_evaluation_script__:1:8
  Stack:
    Error: Evaluation failed: ReferenceError: __awaiter is not defined
        at __puppeteer_evaluation_script__:1:8
        at ExecutionContext.evaluateHandle (/home/sg/git/autumn-leaves/imagemagick-browser/node_modules/puppeteer/lib/ExecutionContext.js:106:13)
        at process._tickCallback (internal/process/next_tick.js:68:7)
        at <Jasmine>
        at ExecutionContext.<anonymous> (/home/sg/git/autumn-leaves/imagemagick-browser/node_modules/puppeteer/lib/helper.js:144:27)
        at ExecutionContext.evaluate (/home/sg/git/autumn-leaves/imagemagick-browser/node_modules/puppeteer/lib/ExecutionContext.js:58:31)
        at ExecutionContext.<anonymous> (/home/sg/git/autumn-leaves/imagemagick-browser/node_modules/puppeteer/lib/helper.js:145:23)
        at Frame.evaluate (