Cannot understand the purpose of ctx.throw's behaviour

const Koa = require('koa')

const app = new Koa()

app.use(async ctx => {
  ctx.throw('aaa')
})
app.listen(4000)

This will throw a real javascript runtime error, and gives requester a response InternalServerError: aaa.

So, the code below looks weird:

try {
    const {username, password} = ctx.request.body
    const user = getUserFromDB(username)
    if (user.password === password) {
      ctx.status = 200
    } else {
      ctx.throw(401, 'Invalid username or password')
      // this information should return to requester directly, but in fact, it was caught by below `catch`, and return a 500 error to the requester.
    }
  } catch (e) {
    ctx.throw(500, 'some other code error')
  }

And there is anther situation: When I use supertest to test my server, when run into ctx.throw(500, 'blabla'), it will shows on test result , it is very ugly…

I known this is cause by I use the koa instance in my test case, but any other best practice? Thanks.

I think , ctx.throw not throw a real javascript runtime error will help above two situation

[jfurfaro]

ctx.throw() throws an error to let the error event handler take control, which by default is set by Koa in order to gracefully respond (which includes any thrown error).

The ctx.throw() method is a convenience that will set err.status to a corresponded HTTP status code (defaulting to 500), as well as set some other properties. See this doc for more info.

[kristiandupont]

For others stumbling upon this, if you are setting your code to a non-official HTTP status code, Koa will sneakily set it to 500: https://github.com/koajs/koa/blob/d48d88ee17b780c02123e6d657274cab456e943e/lib/context.js#L150

This tripped me up for a bit.