CODEWITHSUNDEEP
javascriptpuppeteer
Falko
Falko

Reputation: 1035

Is it possible to pass a function to Puppeteer's page.evaluate()

I am using Puppeteer to parse a webpage and can't find a definitive answer to my question.

I am trying to pass a function as an argument to page.evaluate() An object is OK to pass but can't seem to pass a function. Here's a contrived example:

const obj = {
 thing: 'thing1',
};

const myfunction = () => {
 return `great ${stuff}`;
};

await page.evaluate((obj, function)=>{
 const thing = myfunction;
},(obj, function));

Is it possible to pass a function as an argument to puppeteers page.evaluate()?

Upvotes: 7

Views: 4480

Answers (1)

Thomas Dondorf
Thomas Dondorf

Reputation: 25230

No, you cannot pass functions like that. The passed data needs to be serializable via JSON.stringify, which is not possible for functions.

Alternative: Expose the function

To use a function from your Node.js environment inside the page, you need to expose it via page.exposeFunction. When called the function is executed inside your Node.js environment

await page.exposeFunction('myfunction', text => `great ${text}`);
await page.evaluate(async (object) => {
  return await window.myfunction(object); // 'great example'
}, 'example');

Alternative: Define the function inside page.evaluate

To use a function inside the page context, you can either define it inside of the context. This way, the function does not have access to your Node.js variables.

await page.evaluate((obj) => {
  const myfunction = (stuff) => `great ${stuff}`;
  return myfunction(obj); // 'great example'
}, 'example');

Upvotes: 13

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