javascript - How to pass a function in Puppeteers .evaluate() method?

Question

Whenever I try to pass a function, like this:

var myFunc = function() { console.log("lol"); };

await page.evaluate(func => {
 func();
 return true;
}, myFunc);

I get:

(node:13108) UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 1): Error: Evaluation failed: TypeError: func is not a function
at func (<anonymous>:9:9)
(node:13108) 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.

Why? How to do it correctly?

Thank you!

€: let me clarify: I am doing it this way because I want to find some DOM elements first and use them inside of that function, more like this (simplified):

var myFunc = function(element) { element.innerHTML = "baz" };

await page.evaluate(func => {
  var foo = document.querySelector('.bar');
  func(foo);
  return true;
}, myFunc);

Answer 1

You cannot pass a function directly into page.evaluate(), but you can call another special method (page.exposeFunction), which expose your function as a global function (also available in as an attribute of your page window object), so you can call it when you are inside page.evaluate():

var myFunc = function() { console.log("lol"); };
await page.exposeFunction("myFunc", myFunc);

await page.evaluate(async () => {
   await myFunc();
   return true;
});

Just remember that page.exposeFunction() will make your function return a Promise, then, you need to use async and await. This happens because your function will not be running inside your browser, but inside your nodejs application.

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