SOURCE

let lessons = [
    {
        category:'css',
        title:'层叠样式'
    },
      {
        category:'html',
        title:'超文本标记语言'
    },
      {
        category:'javascript',
        title:'编程语言'
    },
];

let res = lessons.reduce((obj,cur,index)=>{
    obj[`${cur['category']}-${index+1}`]=cur;
    return obj;
},{});


console.log(JSON.stringify(res,null,2));