Q:

TypeError: trying to access 'property' on undefined

I'm stuck on a strange error: when trying to display a state variable, vuejs warns me:
Error in render function: "TypeError: Cannot read property 'token' of undefined"
My state looks like this (in the vuejs extension):
room:Object
    details:Object
        game_id:"1"
        id:914527404
        max_users:5
        messages:Array[0]
        token:"ef6464692f4cce187fe129d7"
        user:Array[1]
    messages:Array[0]
    users:Array[1]

Despite the error, the HTML is still rendered correctly:
<button id="copySharingLink" type="button" class="btn btn-primary waves-effect waves-light" v-bind:data-token="room.details.token">some text</button>

becomes
<button id="copySharingLink" type="button" data-token="ef6464692f4cce187fe129d7" class="btn btn-primary waves-effect waves-light">some text</button>

I have no idea how to rid out of this error, since it's working.

A:

There may be a time when room or room.details is not yet set, and that may be when the error is getting thrown.
Try changing the code from this...
v-bind:data-token="room.details.token"

...to this:
v-bind:data-token="room.hasOwnProperty('details') ? room.details.token : ''"

