dom基础2 — 实现鼠标放大缩小查看图片功能

<script type="text/javascript">
    "use strict";
    var console = window.console;

    // var Event = require("./addEvent.js");

    var dom = document.createElement('div');
    dom.style.width = '600px';
    dom.style.height = '600px';
    dom.style.border = '1px solid gray';
    dom.style.position = 'absolute';
    dom.style.top = '0';
    dom.style.bottom = '0';
    dom.style.left = '0';
    dom.style.right = '0';
    dom.style.margin = 'auto';
    dom.style.overflow = 'hidden';
    document.body.appendChild(dom);


    dom.insertAdjacentHTML('afterbegin','<img src="https://qidian.qpic.cn/qidian_common/349573/9fb9627740f52f4addf43720928e683d/0"/>');

    var img = document.querySelector('img');
    img.style.width = '100%';
    img.style.height = '100%';
    img.style.objectFit = 'cover';

    // 监听鼠标滚轮事件
    var addEvent = (function(window, undefined) {        
        var _eventCompat = function(event) {
            var type = event.type;
            if (type == 'DOMMouseScroll' || type == 'mousewheel') {
                event.delta = (event.wheelDelta) ? event.wheelDelta / 120 : -(event.detail || 0) / 3;
            }
            if (event.srcElement && !event.target) {
                event.target = event.srcElement;    
            }
            if (!event.preventDefault && event.returnValue !== undefined) {
                event.preventDefault = function() {
                    event.returnValue = false;
                };
            }
            /* 
               ......其他一些兼容性处理 */
            return event;
        };
        if (window.addEventListener) {
            return function(el, type, fn, capture) {
                if (type === "mousewheel" && document.mozFullScreen !== undefined) {
                    type = "DOMMouseScroll";
                }
                el.addEventListener(type, function(event) {
                    fn.call(this, _eventCompat(event));
                }, capture || false);
            };
        } else if (window.attachEvent) {
            return function(el, type, fn, capture) {
                el.attachEvent("on" + type, function(event) {
                    event = event || window.event;
                    fn.call(el, _eventCompat(event));    
                });
            };
        }
        return function() {};    
    })(window);        

    var num = 10;
    addEvent(dom, "mousewheel", function(event) {
        if (event.delta < 0) {
            console.log('鼠标向上滚了,图片缩小');
            num--;
            if (num <= 10) {
                num = 10;
                img.style.transform= 'scale(1)';
            } else if (num > 10) {
                img.style.transform= 'scale(' + num/10 + ')';
                console.log(num/10);
            } else {

            }

        } else {
            console.log('鼠标向下滚了,图片放大');
            num++;
            img.style.transform = 'scale(' + num/10 + ')';
            console.log(num/10);
        }
    });


</script>