How to return variable from evaluate function?

Question

How can I return something from evaluate in a variable?

async function myFunction(page, parentID, elementID)
{
  var childElement; 

  await page.evaluate((parentID, elementID) => {
    var parentElement = getParentElement(parentID);
    childElement = parentElement.getChildElement(parentElement, elementID); // SET THIS VALUE TO var childElement ??

  }, parentID, elementID);

  console.log(childElement.id);
}

Here I want to set something in var childElement. How can I do it?

This thing doesn't work. It says that there is no id of undefined.

For future reference: puppeteer has excellent documentation - github.com/puppeteer/puppeteer/blob/main/docs/api.md — Vaviloff
– Vaviloff, Commented Apr 6, 2021 at 13:32

famoha · Accepted Answer · 2021-04-06 11:45:08Z

1

Try this:

async function myFunction(page, parentID, elementID)
{
  var childElement = await page.evaluate((parentID, elementID) => {
    var parentElement = getParentElement(parentID);
    return parentElement.getChildElement(parentElement, elementID); 
  }, parentID, elementID);

  console.log(childElement.id);
}

edited Apr 6, 2021 at 11:45

answered Apr 6, 2021 at 11:34

famoha

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Comments

Ashishssoni · Accepted Answer · 2021-04-06 11:32:08Z

0

Here you are setting values in "childElement" which was empty at first but later you are extracting childElement.id, so thre are possibility that you arent getting id key in childElement. I suggest first use

 console.log(childElement)

so you will know better, which value you are getting. And you are already setting value of childElement by doing this

childElement = parentElement.getChildElement(parentElement, elementID)

Better check this first, see what exactly you are getting by doing this. Since most of the values are undefined, I cant write a code snippet.

answered Apr 6, 2021 at 11:32

Ashishssoni

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Comments

Satwinder Singh · Accepted Answer · 2021-04-06 11:47:47Z

0

// Can you please try using promises ?
async function myFunction(page, parentID, elementID)
{
    return new Promise((resolve, reject) => {
      page.evaluate((parentID, elementID) => {
        var parentElement = getParentElement(parentID);
        var childElement = parentElement.getChildElement(parentElement, elementID);
    
        resolve(childElement)
      }, parentID, elementID);
      }).catch(function (err) {
        return util.returnExceptionAsPromise(err);
      });
}

// And then call this function like this
myFunction(page, parentID, elementID).then(childElement => {
    console.log('childElement', childElement)
})

answered Apr 6, 2021 at 11:47

Satwinder Singh

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4 Comments

famoha Over a year ago

This is literally just the same thing as to when using async/await, you just rewrote the answer in promise format which async/await does the same behind the scene.

Satwinder Singh Over a year ago

@famoha I know but I prefer using promises,, that is why suggested this approach.

famoha Over a year ago

i mean it just over-complicates a simple matter for the person who asked the question. they used async/await so it would be better to probably also give them an answer in the format they probably understand better and easier.

Satwinder Singh Over a year ago

Yup ! Got your point. Your solution looks more relatable to the question. But still I would go with promises in such situation. No offence :)

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