前端开发textarea高度自适应

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html 代码

<!DOCTYPE html>
<html xmlns=”http://www.w3.org/1999/xhtml”>
    <head>
        <meta http-equiv=”Content-Type” content=”text/html; charset=utf-8″ />
        <title>文本框根据输入内容自适应高度</title>
        <style type=”text/css”>
            h2 {
                text-align: center;
                margin: 50px auto;
            }
            #textarea {
                display: block;
                margin: 0 auto;
                overflow: hidden;
                width: 550px;
                font-size: 14px;
                height: 18px;
                line-height: 24px;
                padding: 2px;
            }
            textarea {
                outline: 0 none;
                border-color: rgba(82, 168, 236, 0.8);
                box-shadow: inset 0 1px 3px rgba(0, 0, 0, 0.1),
                    0 0 8px rgba(82, 168, 236, 0.6);
            }
        </style>
        <script>
            /**
             * 文本框根据输入内容自适应高度
             * @param {HTMLElement} 输入框元素
             * @param {Number} 设置光标与输入框保持的距离(默认0)
             * @param {Number} 设置最大高度(可选)
             */
            var autoTextarea = function (elem, extra, maxHeight) {
                        extra = extra || 0;
                        var isFirefox = !!document.getBoxObjectFor || ‘mozInnerScreenX’ in window,
                        isOpera = !!window.opera && !!window.opera.toString().indexOf(‘Opera’),
                        addEvent = function (type, callback) {
                            elem.addEventListener ?
             elem.addEventListener(type, callback, false) :
                            elem.attachEvent(‘on’ + type, callback);
                        },
                        getStyle = elem.currentStyle ? function (name) {
                            var val = elem.currentStyle[name];</p >
                                 if (name === ‘height’ && val.search(/px/i) !== 1) {
             var rect = elem.getBoundingClientRect();
                                    return rect.bottom – rect.top –
                                    parseFloat(getStyle(‘paddingTop’)) –
                                    parseFloat(getStyle(‘paddingBottom’)) + ‘px’;
                                    };
                                 return val;
                                    } : function (name) {
             return getComputedStyle(elem, null)[name];
                                    },
                                    minHeight = parseFloat(getStyle(‘height’));
                                 elem.style.resize = ‘none’;
                                 var change = function () {
             var scrollTop, height,
                                    padding = 0,
                                    style = elem.style;
                                 if (elem._length === elem.value.length) return;
                                    elem._length = elem.value.length;
                                 if (!isFirefox && !isOpera) {
             padding = parseInt(getStyle(‘paddingTop’)) + parseInt(getStyle(‘paddingBottom’));
                                    };
                                    scrollTop = document.body.scrollTop || document.documentElement.scrollTop;
                                 elem.style.height = minHeight + ‘px’;
                                    if (elem.scrollHeight > minHeight) {
             if (maxHeight && elem.scrollHeight > maxHeight) {
             height = maxHeight – padding;
                                    style.overflowY = ‘auto’;
                                    } else {
             height = elem.scrollHeight – padding;
                                    style.overflowY = ‘hidden’;
                                    };
                                    style.height = height + extra + ‘px’;
                                    scrollTop += parseInt(style.height) – elem.currHeight;
                                    document.body.scrollTop = scrollTop;
                                    document.documentElement.scrollTop = scrollTop;
                                    elem.currHeight = parseInt(style.height);
                                    };
                                    };
                                 addEvent(‘propertychange’, change);
                                    addEvent(‘input’, change);
                                    addEvent(‘focus’, change);
                                    change();
                                    };
        </script>
    </head>
    <body>
        <h2>文本框根据输入内容自适应高度</h2>
        <textarea id=”textarea” placeholder=”回复内容”></textarea>
        <script>
            var text = document.getElementById(‘textarea’)
            autoTextarea(text) // 调用
        </script>
    </body>
</html>
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