JS監聽div的resize事件

時間 2019-11-10

原文原文鏈接

原文地址：http://zhangyiheng.com/blog/articles/div_resize.htmlhtml

需求

開發過程當中常常遇到的一個問題就是如何監聽一個div的size變化。
好比我用canvas繪製了一個chart，當canvas的size發生變化的時候，須要從新繪製裏面的內容，這個時候就須要監聽resize事件作處理。canvas

window上雖然能夠添加resize事件監聽，但這並不能知足咱們的需求，由於不少時候，div的size發生了變化，可是window的size並無改變。
不過咱們能夠間接利用window的resize事件監聽來實現對於某個div的resize事件監聽，請看下面具體實現。瀏覽器

對於div的resize事件的監聽，實現方式有不少，好比周期性檢查，經過scroll事件等等，本文主要介紹經過object元素來實現監聽。app

具體實現

/**
 * Created by taozh on 2017/5/6.
 * taozh1982@gmail.com
 */
var EleResize = {
    _handleResize: function (e) {
        var ele = e.target || e.srcElement;
        var trigger = ele.__resizeTrigger__;
        if (trigger) {
            var handlers = trigger.__z_resizeListeners;
            if (handlers) {
                var size = handlers.length;
                for (var i = 0; i < size; i++) {
                    var h = handlers[i];
                    var handler = h.handler;
                    var context = h.context;
                    handler.apply(context, [e]);
                }
            }
        }
    },
    _removeHandler: function (ele, handler, context) {
        var handlers = ele.__z_resizeListeners;
        if (handlers) {
            var size = handlers.length;
            for (var i = 0; i < size; i++) {
                var h = handlers[i];
                if (h.handler === handler && h.context === context) {
                    handlers.splice(i, 1);
                    return;
                }
            }
        }
    },
    _createResizeTrigger: function (ele) {
        var obj = document.createElement('object');
        obj.setAttribute('style',
            'display: block; position: absolute; top: 0; left: 0; height: 100%; width: 100%; overflow: hidden;opacity: 0; pointer-events: none; z-index: -1;');
        obj.onload = EleResize._handleObjectLoad;
        obj.type = 'text/html';
        ele.appendChild(obj);
        obj.data = 'about:blank';
        return obj;
    },
    _handleObjectLoad: function (evt) {
        this.contentDocument.defaultView.__resizeTrigger__ = this.__resizeElement__;
        this.contentDocument.defaultView.addEventListener('resize', EleResize._handleResize);
    }
};
if (document.attachEvent) {//ie9-10
    EleResize.on = function (ele, handler, context) {
        var handlers = ele.__z_resizeListeners;
        if (!handlers) {
            handlers = [];
            ele.__z_resizeListeners = handlers;
            ele.__resizeTrigger__ = ele;
            ele.attachEvent('onresize', EleResize._handleResize);
        }
        handlers.push({
            handler: handler,
            context: context
        });
    };
    EleResize.off = function (ele, handler, context) {
        var handlers = ele.__z_resizeListeners;
        if (handlers) {
            EleResize._removeHandler(ele, handler, context);
            if (handlers.length === 0) {
                ele.detachEvent('onresize', EleResize._handleResize);
                delete  ele.__z_resizeListeners;
            }
        }
    }
} else {
    EleResize.on = function (ele, handler, context) {
        var handlers = ele.__z_resizeListeners;
        if (!handlers) {
            handlers = [];
            ele.__z_resizeListeners = handlers;

            if (getComputedStyle(ele, null).position === 'static') {
                ele.style.position = 'relative';
            }
            var obj = EleResize._createResizeTrigger(ele);
            ele.__resizeTrigger__ = obj;
            obj.__resizeElement__ = ele;
        }
        handlers.push({
            handler: handler,
            context: context
        });
    };
    EleResize.off = function (ele, handler, context) {
        var handlers = ele.__z_resizeListeners;
        if (handlers) {
            EleResize._removeHandler(ele, handler, context);
            if (handlers.length === 0) {
                var trigger = ele.__resizeTrigger__;
                if (trigger) {
                    trigger.contentDocument.defaultView.removeEventListener('resize', EleResize._handleResize);
                    ele.removeChild(trigger);
                    delete ele.__resizeTrigger__;
                }
                delete  ele.__z_resizeListeners;
            }
        }
    }
}

測試代碼：ide

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Resize</title>
    <script src="./EleResize.js"></script>
    <style>
        html, body {
            margin: 0;
            padding: 0;
            width: 100%;
            height: 100%;
        }

        #resizeDiv {
            width: 60%;
            height: 60%;
            border: 1px solid red;
            margin: 20px;
        }

        button {
            margin: 20px 20px 0;
        }
    </style>
</head>
<body>
<button onclick="addListener()">addListener</button>
<button onclick="removeListener()">removeListener</button>
<button onclick="resize()">resize</button>
<div id="resizeDiv"></div>
<script>
    var resizeDiv = document.getElementById('resizeDiv');
    function resize() {
        resizeDiv.style.width = "200px";
    }
    var listener = function () {
        console.log("resize");
    };
    function addListener() {
        EleResize.on(resizeDiv, listener);
    }
    function removeListener() {
        EleResize.off(resizeDiv, listener)
    }
</script>
</body>
</html>

View Code

原理

這裏的具體實現分兩類，測試

ie9-10

　　　　默認支持div的resize事件，能夠直接經過div.attachEvent('onresize', handler);的方式實現this

其它瀏覽器

　　　　經過在div中添加一個內置object元素實現監聽。
　　　　設置object元素的style使其填充滿div，這樣當div的size發生變化時，object的size也會發生變化。
　　　　而後監聽object元素的contentDocument.defaultView(window對象)的resize事件。spa

注：本文提供的是如何監聽resize事件，其實在resize時，可能會連續快速的觸發(好比拖動瀏覽器)，爲了提升效率，能夠考慮使用批處理的模式。code