Search code examples
javascriptnode.jsnightmare

nightmare - where does document come from?

The code snippet below is an example from https://github.com/segmentio/nightmare

const Nightmare = require('nightmare')
const nightmare = Nightmare({ show: true })

nightmare
  .goto('https://duckduckgo.com')
  .type('#search_form_input_homepage', 'github nightmare')
  .click('#search_button_homepage')
  .wait('#r1-0 a.result__a')
  .evaluate(() => document.querySelector('#r1-0 a.result__a').href)
  .end()
  .then(console.log)
  .catch(error => {
    console.error('Search failed:', error)
  })

I can't wrap my mind around this line:

.evaluate(() => document.querySelector('#r1-0 a.result__a').href)

Where does the document come from? The code is running on Node.js, so no browser context. I've checked that the document is not a global variable. Clearly not a parameter too. I've also verified that the example code works. How is it possible?

Solution

  • That arrow function is passed as a parameter to be run in the Nightmare headless browser, where document is defined.

    .evaluate(() => document.querySelector('#r1-0 a.result__a').href)

    You can also pass extra arguments to this function like so:

    .evaluate((arg) => {
  document.querySelector('#r1-0 a.result__a').href);
}, 'test');