const Koa = require('koa');
const app = new Koa();
const json = require('koa-json')
let Router = require('koa-router');
let router = new Router();


let users = [
    { name: 'Kevin', email: 'k@gmail.com' },
    { name: 'Star', email: 'sss@gmail.com' },
    { name: 'Vick', email: 'V@gmail.com' },
]

router
    .get('/user', list)
    .get('/user/:id', detail)
    .post('/user/:id', update)
    .post('/user/create', create)

function list(ctx) {
    ctx.body = users
}

function detail(ctx) {
    ctx.body = users[ctx.params.id]
}

function create(ctx) {
    new_user = ctx.request.body
    users.push(new_user)
    ctx.body = users
}

function update(ctx) {
    ctx.body = Object.assign(users[ctx.params.id], ctx.request.body)
}

TypeError: Cannot convert undefined or null to object
      at Function.assign (<anonymous>)
      at update (E:projectjavascriptnodejsKoaAPIpersonserver.js:38:20)

router
    .get('/user', list)
    .get('/user/:id', detail)
    .post('/user/create', create)
    .post('/user/:id', update)