Fading an element using only Javascript

/** * Fade an HTMLElement to a specific value using style attributes *  * @param HTMLElement element * @param number toValue * @param number duration * @return void */function fadeTo(element, toValue = 0, duration = 200) {    // Store our element's current opacity     // (or default to 1 if null)    const fromValue = parseFloat(element.style.opacity) || 1;    // Mark the start time (in ms). We use this to calculate    // a ratio over time that applied to our supplied duration     // argument    const startTime = Date.now();    // Determines time (ms) between each frame. Sometimes you     // may not want a full 60 fps for performance reasons or     // aesthetic     const framerate = 1000 / 60; // 60fps    // Store reference to interval (number) so we can clear     // it later    let interval = setInterval(() => {        const currentTime = Date.now();        // This creates a normalized number between now vs when we        // started and how far into our desired duration it goes        const timeDiff = (currentTime - startTime) / duration;        // Interpolate our values using the ratio from above        const value = fromValue - (fromValue - toValue) * timeDiff;        // If our ratio is >= 1, then we're done..         // so stop processing        if (timeDiff >= 1) {            clearInterval(interval);            interval = 0;        }        // Apply visual. Style attributes are strings.        element.style.opacity = value.toString();    }, framerate)}// Element referenceconst element = document.querySelector('div');// Fade in and out on clickelement.addEventListener('click', e => {    // Animates our element from current opacity (1.0) to 0.25 for 1000ms    fadeTo(element, 0.25, 1000);    // Waits 1s, then animates our element's opacity to 1.0 for 500ms    setTimeout(() => {        fadeTo(element, 1.0, 500);    }, 1000);});