In Vue.js, the data is passed to child components from the parent component using a prop or a custom attribute. This custom attribute becomes a property on the child component instance. This procedure is called a one-way data flow.
Once the parent component updates a prop value, the child component is automatically updated. The child component can communicate back to the parent via an event, but mutating a property inside a child component should not be done. It does not affect the parent component also unless it is an object or array. When the child component instance emits an event, the parent assigns a handler to that event, and data is passed back to the parent.