Error details for UnhandledPromiseRejectionWarning

Steps to reproduce

Tell us about your environment:

• Puppeteer version: 1.17.0
• Platform / OS version: WSL (Bash on Windows)
• Node.js version: v12.4.0

What steps will reproduce the problem?

const clickAndWait = function(container, target, btn) {
    return container.evaluate((target, btnNext) => {
        return new Promise((resolve, reject) => {
            let observer = new MutationObserver(function() {
                observer.disconnect(); // use the mutation observer only once
                resolve();
            });
            observer.observe(target, { childList: true, subtree: true, });

            // some reasonable timeout, in case loading got stuck
            setTimeout(reject.bind(this, 'timeout'), 5000);

            // puppeteer click() doesn't work, must use native click() in eval
            btn.click();
        });
    }, target, btn);
};

await ph.clickAndWait(iframe, someContainer, btnNext);

What is the expected result? The function evaluates, MutationObserver is set up, the button is clicked, MutationObserver resolves the Promise and await proceeds.

What happens instead? Error:

(node:4335) UnhandledPromiseRejectionWarning: Error: Evaluation failed: [object Object]
    at ExecutionContext._evaluateInternal (/d/DATA/WDH/Webseite/workspaces/Ari/www/application/noch-frei/crawl/puppeteer-launch/node_modules/puppeteer/lib/ExecutionContext.js:122:13)

(node:4335) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block or by rejecting a promise which was not handled with .catch(). (rejection id: 1)
(node:4335) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

How to catch the Promise exception and log the Object so I can read the error messages or at least find out what failed during the evaluation?

Also, this helper method worked in the past, after changing some of the code and moving its invocations, this error occurs.

[aslushnikov]

Indeed, we do horrible job showing some errors 🤦‍♂️

For example, the following doesn’t tell me why exactly evaluation has failed:

const puppeteer = require('puppeteer');

puppeteer.launch().then(async browser => {
  const page = await browser.newPage();
  await page.evaluate(() => new Promise(() => {
    does_not_exist.click();
  })).catch(e => {
    console.log(e);
  });
  await browser.close();
})

Gives me an error:

aslushnikov:~/prog/puppeteer(master)$ node a.js
Error: Evaluation failed: [object Object]
    at ExecutionContext._evaluateInternal (/Users/aslushnikov/prog/puppeteer/lib/ExecutionContext.js:122:13)
    at processTicksAndRejections (internal/process/task_queues.js:85:5)
    at async ExecutionContext.evaluate (/Users/aslushnikov/prog/puppeteer/lib/ExecutionContext.js:48:12)
    at async /Users/aslushnikov/prog/puppeteer/a.js:5:3
  -- ASYNC --
    at ExecutionContext.<anonymous> (/Users/aslushnikov/prog/puppeteer/lib/helper.js:111:15)
    at DOMWorld.evaluate (/Users/aslushnikov/prog/puppeteer/lib/DOMWorld.js:112:20)
    at processTicksAndRejections (internal/process/task_queues.js:85:5)
  -- ASYNC --
    at Frame.<anonymous> (/Users/aslushnikov/prog/puppeteer/lib/helper.js:111:15)
    at Page.evaluate (/Users/aslushnikov/prog/puppeteer/lib/Page.js:782:43)
    at Page.<anonymous> (/Users/aslushnikov/prog/puppeteer/lib/helper.js:112:23)
    at /Users/aslushnikov/prog/puppeteer/a.js:5:14
    at processTicksAndRejections (internal/process/task_queues.js:85:5)

Not a single word about ReferenceError!

Whereas CDP does tell us the reason:

aslushnikov:~/prog/puppeteer(master)$ DEBUG=* node a.js
....
  puppeteer:protocol SEND ► {"sessionId":"EE1E9F39496DD1867256AC7E74527119","method":"Runtime.callFunctionOn","params":{"functionDeclaration":"() => {\n      btn.click();\n  }\n//# sourceURL=__puppeteer_evaluation_script__\n","executionContextId":1,"arguments":[],"returnByValue":true,"awaitPromise":true,"userGesture":true},"id":16} +1ms
  puppeteer:protocol ◀ RECV {"id":16,"result":{"result":{"type":"object","subtype":"error","className":"ReferenceError","description":"ReferenceError: btn is not defined\n    at __puppeteer_evaluation_script__:2:7","objectId":"{\"injectedScriptId\":1,\"id\":1}"},"exceptionDetails":{"exceptionId":1,"text":"Uncaught","lineNumber":1,"columnNumber":6,"scriptId":"11","stackTrace":{"callFrames":[{"functionName":"","scriptId":"11","url":"__puppeteer_evaluation_script__","lineNumber":1,"columnNumber":6}]},"exception":{"type":"object","subtype":"error","className":"ReferenceError","description":"ReferenceError: btn is not defined\n    at __puppeteer_evaluation_script__:2:7","objectId":"{\"injectedScriptId\":1,\"id\":2}"}}},"sessionId":"EE1E9F39496DD1867256AC7E74527119"} +1ms
.....

[brillout]

Indeed, we do horrible job showing some errors For example, the following doesn’t tell me why exactly evaluation has failed

Anything new on that end?

I still can’t get puppeteer to show me browser-side errors, which is particularly inconvenient when considering puppeteer an automation tool for unit testing 😞.

Other than that, thanks for this lovely tool.