this.checklist.filter(x=> x.isSelected).map(y =>{ return y.catItem }).join(", ")
const data = [{id: 111}, {id: 22222, a:222}, {id:333,a:3}];
console.log(Object.keys(data).map(key => `${key}: ${data[key].id}`).join(","));
// 0: 111, 1: 22222, 2: 333