怎么通过onclick事件获取js函数返回值（代码少）

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;}