To get all the email from links with 'mailto' action with javascript.

getallmail.js

var links = document.getElementsByTagName('a'), hrefs = [], sendIt = '';
for (var i = 0; i<links.length; i++)
{   
    if(links[i].href.includes('mailto')) {
      var email = links[i].href.replace('mailto:','');
      //If you want to use this as array
      hrefs.push(email);
      
      //If you want to copy all email ids in one string (usually to send mail to multiple ids at once)
      sendIt += email + ', ';
    }
}

// Auto-Copy e-mail from string
var el = document.createElement('textarea');
el.value = sendIt;
el.setAttribute('readonly', '');
el.style = {display: 'none'};
document.body.appendChild(el);
el.select();
document.execCommand('copy');
document.body.removeChild(el);