Why do errors in Vue router beforeEach throw no exception when running in V8Js?

Question

I have a Laravel / Vue app using SSR so have JavaScript running server side and client side.

I had a bug in my code where I was checking user.id when the user object was null.

If this had been running client side I would have seen the error in the console and easily fixed it.

However because this was running in v8js I got no output at all and was just a case of trial and error to locate and fix the bug. This reminded me of fixing JS errors in IE6 - not something I want to repeat!

I did try the getPendingException() method but this just gave me a warning about it being deprecated.

Note some errors are generated....

Obvious syntax errors are picked up straight away when I run webpack.

Some errors throw a V8JsScriptException:

if(foo.bar) {}

This generates the error:

V8Js::compileString():86354: ReferenceError: foo is not defined

If I wrap foo in a function and then call it:

function test() {
    if(foo.bar) {}
}
test()

No exception is thrown, but the only output returned is:

ReferenceError: foo is not defined

However this code that is for my Vue router produces no output at all:

import Vue from 'vue'
import Router from 'vue-router'
import routes from './routes'

Vue.use(Router)

export function createRouter () {
    const router = new Router({
        mode: 'history',
        routes: routes
    })

    router.beforeEach(async (to, from, next) => {
        if(foo.bar) {}
        next()
    })

    return router
}

When I run this same code in the browser the console shows:

ReferenceError: foo is not defined

So it seems JS is creating an error - but somehow V8Js is not passing it on.

Why does the undefined error in the Vue router not throw an exception when run in v8js?

Never used v8js but from the docs it seems wrapping your code in a [V8JsException](https://www.php.net/manual/en/class.v8jsexception.php) and catching it might give you a clue if an error occurs. [Here's](https://dzone.com/articles/running-javascript-inside-php) also a short tutorial mentioning catching exceptions. — SaschaM78, May 27 '20 at 15:10
Sometimes an V8JsException is thrown - but sometimes not. I've updated my question to describe the problem in more depth. — Felix Eve, May 28 '20 at 07:33

score 1 · Answer 1 · answered Jun 04 '20 at 16:23

1

Use an onError handler on your router: router.onError

And, since your beforeEnter guard is async, you'll need to call next with the error:

export function createRouter () {
    const router = new Router({
        mode: 'history',
        routes: routes
    })

    router.beforeEach(async (to, from, next) => {
      try {
        if(foo.bar) {}
        next()
      } catch (e) {
        next(e)
      } 
    })

    router.onError(err => {
       print('<!-- router error: ' + err.message + ' -->')
    })

    return router
}

For your example, you could use a synchronous guard and do without the try/catch:

router.beforeEach((to, from, next) => {
    if(foo.bar) {}
    next()
})

answered Jun 04 '20 at 16:23

wmjasonward

21
2

This logic seems flawless - however it's not actually producing any output for me. However I'm still going to keep this in my code just in case it ever picks anything up. – Felix Eve Jun 05 '20 at 08:41
I have a similar situation where `renderVueComponentToString` returns an empty string and no exceptions are thrown. For me, it happens on a component with a specific vue-apollo smart query. It works without error on the client, but seems to bomb during ssr. I traced into vue-server-renderer-basic.js but without the ability to connect a debugger to v8js I wasn't able to figure it out either. I did try your example of the undefined variable `foo` with the `onError` handler and the `onError` handler picked it up for me. Whatever is causing this is very obscure. – wmjasonward Jun 05 '20 at 16:15
@FelixEve - Rebuilding v8 and v8js (I went to versions 8.5.77 and 2.1.1, respectively) solved the problem for me. – wmjasonward Jun 06 '20 at 14:24

Why do errors in Vue router beforeEach throw no exception when running in V8Js?

1 Answers1