Native javascript implements image scrolling and delayed loading functions

This article mainly introduces the use of native javascript to implement image scrolling and delayed loading functions. The ideas and methods are shared with everyone. I hope it will be helpful to everyone.

Achievement effect: when the scroll bar is pulled down, the image will not start loading until it appears in the visible area

Idea:

(1) img tag, put the real image address, Put it in the properties you set, such as lazy-src

(2) Get the height of img from the page (offset().top in JQ), the native one is:

img. getBoundingClientRect().top document.body.scrollTop||document.documentElement.scrollTop

(3) Determine whether the position where img appears is in the visible area:

is in the visible area of ​​the browser, justTop>scrollTop&&offsetTop

//保存document在变量里，减少对document的查询
            var doc = document;
            for(var n=0,i = this.oImg.length;n<i;n++){
                //获取图片占位符图片地址
                var hSrc = this.oImg[n].getAttribute(this.sHolder_src);
                if(hSrc){
                    var scrollTop = doc.body.scrollTop||doc.documentElement.scrollTop,
                        windowHeight = doc.documentElement.clientHeight,
                        offsetTop = this.oImg[n].getBoundingClientRect().top + scrollTop,
                        imgHeight = this.oImg[n].clientHeight,
                        justTop = offsetTop + imgHeight;
                    // 判断图片是否在可见区域
                    if(justTop>scrollTop&&offsetTop<(scrollTop+windowHeight)){

                        this.isLoad(hSrc,n);
                    }
                }
            }

The following is the detailed code:

function LGY_imgScrollLoad(option){
        this.oImg = document.getElementById(option.wrapID).getElementsByTagName('img');
        this.sHolder_src = option.holder_src;
        this.int();
    }
    LGY_imgScrollLoad.prototype = {
        loadImg:function(){
            //保存document在变量里，减少对document的查询
            var doc = document;
            for(var n=0,i = this.oImg.length;n<i;n++){
                //获取图片占位符图片地址
                var hSrc = this.oImg[n].getAttribute(this.sHolder_src);
                if(hSrc){
                    var scrollTop = doc.body.scrollTop||doc.documentElement.scrollTop,
                        windowHeight = doc.documentElement.clientHeight,
                        offsetTop = this.oImg[n].getBoundingClientRect().top + scrollTop,
                        imgHeight = this.oImg[n].clientHeight,
                        justTop = offsetTop + imgHeight;
                    // 判断图片是否在可见区域
                    if(justTop>scrollTop&&offsetTop<(scrollTop+windowHeight)){
                        //alert(offsetTop);
                        this.isLoad(hSrc,n);
                    }
                }

            }
        },
        isLoad:function(src,n){
            var src = src,
                n = n,
                o_img = new Image(),
                _that = this;
            o_img.onload = (function(n){
                _that.oImg[n].setAttribute(&#39;src&#39;,src);
                _that.oImg[n].removeAttribute(_that.sHolder_src);
            })(n);
            o_img.src = src;
        },
        int:function(){
            this.loadImg();
            var _that = this,
                timer = null;
            // 滚动：添加定时器，防止频繁调用loadImg函数
            window.onscroll = function(){
                clearTimeout(timer);
                timer = setTimeout(function(){
                    _that.loadImg();
                },100);
            }
        }
    }

Rendering:

The above is the entire content of this chapter. For more related tutorials, please visit JavaScript Video Tutorial!