How to get the return value of js function through onclick event (less code)_Basic knowledge

The specific process will not be described in detail, just go to the code:

Writing a pop-up box and binding the onclick event seems to be unable to control its return value. The code is as follows

function createBtn(){ 
for(var i = 0; i < _this.btn.length; i++){
var btn = document.createElement('span');
btn.id = 'btn_' + i;
btn.innerHTML = _this.btn[i];
btn.style.padding = '5px 15px';
btn.style.background = '#E5E5E5';
btn.style.borderRadius = '5px';
btn.style.marginRight = '15px';
btn.style.cursor = 'pointer';
document.getElementById('btn_box').appendChild(btn); 
//btn.onclick = closeBox;
} 
}
function closeBox(){
var box = document.getElementById('msg_box');
box.remove(); 
if(this.id == 'btn_0'){
isBool = true;
}else{
isBool = false;
}
return isBool;
}

The above code is all the code to obtain the return value of the js function through the onclick event. I hope it will be helpful to everyone's future study work.