The variable "vue" is not properly defined within the instance, yet it is being called

I'm currently working on a Vue app and encountering an issue. The onScroll function is working correctly, but when I click the button component to trigger the sayHello function, I receive an error message.

The error states: "Property or method 'sayHello' is not defined on the instance but referenced during render. Make sure to declare reactive data properties in the data option."

Vue.component('test-item', {
    template: '<div><button v-on:click="sayHello()">Hello</button></div>'
});

var app = new Vue({
    el: '#app',
    data: {
        header: {
            brightness: 100
        }
    },
    methods: {
        sayHello: function() {
            console.log('Hello');
        },
        onScroll: function () {
            this.header.brightness = (100 - this.$el.scrollTop / 8);
        }
    }
});

I have tried to resolve this issue by searching for solutions, but haven't had any luck so far. Any assistance would be greatly appreciated.

Thank you.

Answer №1

With the exception of certain cases (primarily involving props), every component operates independently from one another. They have their own distinct data, variables, functions, and more. This also applies to their methods.

As a result, the test-item component does not include a sayHello method.

Answer №2

To resolve the warning, make sure to use .mount('#app') after creating the Vue instance instead of the el attribute.

Take a look at the code snippet below;

var app = new Vue({
    data: {
        header: {
            brightness: 100
        }
    },
    methods: {
        sayHello: function() {
            console.log('Hello');
        },
        onScroll: function () {
            this.header.brightness = (100 - this.$el.scrollTop / 8);
        }
    }
}).mount('#app');

Keep in mind; although it may not be mandatory, I tried using it while attempting to address the same problem with the Laravel Elixir Vue 2 project.

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