index.js

import TWEEN from '@tweenjs/tween.js';

export default (propName, duration = 500, ease = TWEEN.Easing.Quadratic.Out) => {
    const propNameTween = `${propName}Tween`;

    return {
        data() {
            return {
                [propNameTween]: this[propName],
            };
        },
        watch: {
            // watch when the prop changes and tween the tween prop from old to new
            [propName](newValue, oldValue) {
                new TWEEN.Tween({
                    number: oldValue,
                })
                    .to({
                        number: newValue,
                    }, duration)
                    .easing(ease)
                    .onUpdate(tween => {
                        this[propNameTween] = tween.number;
                    })
                    .start();

                animate();
            },
        },
    };
};

function animate() {
    if (TWEEN.update()) {
        requestAnimationFrame(animate);
    }
}