文本框高度自适应

1.contenteditable---并不支持表单事件

onkeyup模拟placeholder,但是只能输入第一个字生效

<div name="" id="add-msg" contenteditable="true" class="placeholder" ></div>
css:.msg-content #add-msg.placeholder:after{
    content: '我来说两句';
    color: #999;
}

JS： $('#add-msg').keyup(function(){
      $(this).removeClass('placeholder');
    });

2.textarea自适应--ie下光标会闪动

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        h3 {
            text-align: center;
        }
        #textarea{
            display: block;
            margin: 0 auto;
            height: 18px;
            font-size: 16px;
            line-height: 24px;
            width: 400px;
            padding: 4px;
        }
        textarea {
            letter-spacing: normal;
            word-spacing: normal;
            border: 1px solid #ccc;
            overflow-wrap: break-word;
            overflow:hidden;
            resize: none;
            outline: 0;
        }
    </style>
</head>
<body>
 <h3>文本框高度自适应</h3>
    <textarea id="textarea"  name="" placeholder="输入框"></textarea>
<script>
    var text= document.getElementById("textarea");
    autoTextarea(text);
    /**
     * 文本框根据输入内容自适应高度
     * elem                {HTMLElement}        输入框元素
     * extra               {Number}                设置光标与输入框保持的距离(默认0)
     * maxHeight               {Number}                设置最大高度(可选)
     */
 function autoTextarea(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];

                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>
</body>
</html>

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