SOURCE

const images = document.querySelectorAll('img')

const callback = (entries) => {
    entries.forEach(enter =>{
        if(enter.isIntersectiing){
            const image = enter.target;
            const data_src = image.getAttribute('data_src')
            image.setAttribute('src',data_src)
            observer.unobserve(img)
        }
    })
}

const observer = new IntersectionObserver(callback)

images.forEach( image =>{
    observer.observer(img)
})