javascript - Pass Class as an Argument to page.evaluate in Puppeteer - Stack Overflow

admin管理员组

文章数量:1334282

In Puppeteer, page.evaluate throws an error if I pass a class as an argument.

It works for regular objects though.

Is there some workaround to make it work?

const puppeteer = require("puppeteer");

(async () => {
let browser = await puppeteer.launch({
    headless: true
});
let page = await browser.newPage();
class SomeClass {
    constructor() {
        this.a = 3;
    }
}
await page.evaluate((SomeClass) => {
    let object = new SomeClass();
    console.log(object.a);
}, SomeClass);
})();

In Puppeteer, page.evaluate throws an error if I pass a class as an argument.

It works for regular objects though.

Is there some workaround to make it work?

const puppeteer = require("puppeteer");

(async () => {
let browser = await puppeteer.launch({
    headless: true
});
let page = await browser.newPage();
class SomeClass {
    constructor() {
        this.a = 3;
    }
}
await page.evaluate((SomeClass) => {
    let object = new SomeClass();
    console.log(object.a);
}, SomeClass);
})();

• javascript
• puppeteer

Share Improve this question Follow edited Jul 16, 2018 at 17:36 Grant Miller 29.1k1616 gold badges155155 silver badges168168 bronze badges asked Jul 16, 2018 at 6:59 yewangyewang 64511 gold badge88 silver badges1818 bronze badges 1

• Answer depends on how would you evaluate a class? Define that and edit the question to include this information and I'll help you reach a working solution – Adelin Commented Jul 16, 2018 at 7:03

Add a ment  | 

2 Answers 2

Sorted by: Reset to default 7

There is a similar problem if you try to pass a function. I've seen people stringifying the function to pass it to puppeteer to make it work, so in your case I'd do this using eval. Many people think eval is evil, maybe there is a better way, but at least it's a possible workaround.

class SomeClass {
    constructor() {
        this.a = 3;
    }
}    
await page.evaluate((strSomeClass) => {
    eval("window.SomeClass = " + strSomeClass);
    let object = new SomeClass();
    console.log(object.a);
}, SomeClass.toString());

You can avoid using eval() by passing an instance of the object, rather then the object itself, to page.evaluate():

await page.evaluate(object => {
  console.log(object.a);
}, new SomeClass);

Your full program should look something like this:

'use strict';

const puppeteer = require('puppeteer');

(async () => {
  const browser = await puppeteer.launch({
    headless: true,
  });

  const page = await browser.newPage();

  class SomeClass {
    constructor() {
      this.a = 3;
    }
  }

  await page.evaluate(object => {
    console.log(object.a);
  }, new SomeClass);

  await browser.close();
})();

本文标签： javascriptPass Class as an Argument to pageevaluate in PuppeteerStack Overflow