gistfile1.txt

// getBoundingClientRect
let imgList1 = [...document.querySelectorAll(".get_bounding_rect")]
let num = imgList1.length

let lazyLoad1 = (function () {
    let count = 0
    return function () {
        let deleteIndexList = []
        imgList1.forEach((img,index) => {
            let rect = img.getBoundingClientRect()
            if (rect.top < window.innerHeight) {
                img.src = img.dataset.src
                // Add picture to delete list after loading successfully
                deleteIndexList.push(index)
                count++
                if (count === num) {
                    //When all pictures are loaded, unbind scroll event
                    document.removeEventListener('scroll',lazyLoad1)
                }
            }
        })
        // Delete loaded pictures
        imgList1 = imgList1.filter((_,index)=>!deleteIndexList.includes(index))

    }
})()