原生javascript实现图片滚动、延时加载功能

实现效果：下拉滚动条时，图片出现在可见区域时，才开始加载
思路：
（1）img标签，把真实的图片地址，放在自己设置的属性里面，如 lazy-src
（2）获取img离页面的高度（在JQ里是offset().top），原生是：
　　 img.getBoundingClientRect().top + document.body.scrollTop||document.documentElement.scrollTop
（3）判断img出现的位置是否在可见区域里:
　　.在浏览器的可见区域，justTop>scrollTop&&offsetTop<(scrollTop+windowHeight)，这里的justTop是图片的offsetTop+图片高度


代码如下:


//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);                     }                 }
            }


以下为详细代码：


代码如下:


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('src',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);             }         }     }


效果图：

以上就是本文的全部内容了，实现的效果不比jQuery插件实现的差吧，代码还简洁，小伙伴们参考下吧。


有用  |  无用 取消

猜你喜欢