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

//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：

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。