trick

let counterLabel=document.getElementById("counter");let count=0;let username=document.getElementById("username").value;function*generate(email){if(email.length<=1){yield email;}else{let head=email[0];let tail=email.slice(1);for(let item of generate(tail)){yield head+item;yield head+'.'+item;}}}
function updateEmails(){let username=document.getElementById("username").value;document.getElementById("emails").value='';count=0;let startTime=new Date();for(let message of generate(username)){document.getElementById("emails").value+=message+'@gmail.com\r\n';count+=1;counterLabel.innerText='Generated: '+count;}
document.getElementById("emails").value=document.getElementById("emails").value.slice(0,-1);let endTime=new Date();let timeDiff=endTime-startTime;console.log('Finished in '+timeDiff+'ms');}
document.getElementById("username").oninput=function(){let newUsername=document.getElementById("username").value;if(username!==newUsername){username=newUsername;if(username.length>1){setTimeout(updateEmails,150);}}};document.getElementById("save").onclick=function(){blob=new Blob([document.getElementById('emails').value],{type:"text/plain;charset=utf-8",endings:"transparent"});FileSaver.saveAs(blob,document.getElementById('username').value+".txt");};