Livewire the page has expired when setting properties or calling methods

I'm trying to follow the instructions given in the Livewire docs to set livewire component properties or call methods in javascript. However, I keep getting "Page has expired" alert on Chrome?

<script>
            document.addEventListener('livewire:load', function () {
                //These work:
                console.log(Livewire.first().foo)
                console.log(@this.foo)


                // These give the "The page has expired " error and freeze the page:
                Livewire.first().bar()
                @this.bar()
                Livewire.first().foo = 'Hello world'

            })
</script>