scrape-email.js

document.documentElement.textContent               // Get all of the text content on the web page.
  .replace(/\b(\s*\[at\]\s*)\b/g, '@')             // Replace any ' [at] ' with '@'.
  .split(/\s+/)                                    // Split text content by whitespace between words.
  .filter(Boolean)                                 // Eliminate any empty words.
  .filter(string => {                              // Filter list of words:
    const input = document.createElement('input')  //   by creating an <input> element,
    input.type = 'email'                           //   setting the input type to email,
    input.value = string.trim()                    //   setting its value to the current word,
    return input.checkValidity()                   //   and checking if it's a valid email address.
  })                                               // Result: a list of all valid emails on the page.