html+css+Jquery 实现文本域文字数量限制、根据输入字数自适应高度

先看效果：初始的效果，样式多少有点问题，不重要！重要的是功能！

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输入后：根据文字长度，决定文本域长度 + 限制文字数量

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话不多说，直接上代码！

<!DOCTYPE html>
<html>
<head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1"><title></title>
</head>
<style type="text/css">
.foot-send-img img {width: 20px;height: 20px;
}
.text-input_5ZOdm{display: flex;justify-content: center;align-items: end;position: relative;box-sizing: border-box;font-family: Arial,Helvetica,sans-serif;width: 649px;height: 40px;background: #FFFFFF;box-shadow: 0px 0px 6px 1px #ee1903;border-radius: 10px;
}
.text-container{width: 100%;height:100%;
}
.text-input-textarea_chat{background: #FFFFFF;line-height: 28px;border-radius: 10px;resize: none;outline-color: #ffff;width: 100%;height: 100%;border: none;outline: none;word-break: break-word;font-size: 16px;overflow: hidden;padding-left: 14px;padding-top: 7px;
}
.chat-number{float: right;position: relative;font-size: 12px;font-family: PingFangSC, PingFang SC;font-weight: 400;color: #D1D1D1;bottom: 22px;margin-right: 10px;
}
.foot-send-img{width: 55px;background: #FFA245;border-radius: 8px;display: flex;align-items: center;justify-content: center;cursor: pointer;height: 34px;bottom: 3px;position: relative;
}
.sidebar_right-left{display: flex;align-items: center;padding-left: 76px;
}
</style>
<body>
<div class="sidebar_right-left"><div class="text-input_5ZOdm  text-enable_3rWFc"> <div class="text-container"><textarea class="text-input-textarea_chat chat-input-size" id="chat-input-size" placeholder="请问我 您想了解的问题" maxlength="50"></textarea><p class="chat-number"><span id="textNum">0</span>/<span>50</span></p></div><div class="foot-send-img" id="send-btn"><img src="./images/img1.jpg" align="middle"  class="chat-foot-send"></div>
</div>
</div>
</body>
<script src="https://code.jquery.com/jquery-3.6.0.min.js"></script>
<script type="text/javascript">$("#chat-input-size").on('focus input',function(){var textarea = $('#chat-input-size');computerTextareaRows(textarea);var text = textarea.val();var counter = text.length;if (text.indexOf("请问我您想了解的问题") > -1){textarea.val('')}$("#textNum").text(counter);if(counter >= 50){$('.chat-number').css('color','#FF7F7F');return false;}else{$('.chat-number').css('color','#D1D1D1');}
}).on('blur',function(){var textarea = $('#chat-input-size');var text = textarea.val();if (text === ''){textarea.val('请问我您想了解的问题')}
})//根据texarea行数设置高度
function computerTextareaRows(textarea) {var lineHeight = parseFloat(textarea.css('line-height'));var paddingTop = parseFloat(textarea.css('padding-top'));var paddingBottom = parseFloat(textarea.css('padding-bottom'));// 计算行数var contentHeight = textarea[0].scrollHeight - paddingTop - paddingBottom;let proportion = contentHeight / lineHeight;var rows = proportion < 2 ? 1 : Math.ceil(contentHeight / lineHeight);// console.log(rows,textarea[0].scrollHeight,proportion)if (rows>1){$('#chat-input-size').css('height','40px');$('.text-input_5ZOdm').css('height', 'auto');$('.text-input_5ZOdm').css('height', textarea[0].scrollHeight+'px');$('#chat-input-size').css('height',textarea[0].scrollHeight+'px');// $('#send-btn').css('margin-top','20px');} else {$('.text-input_5ZOdm').css('height','40px');// $('#send-btn').css('margin-top','0px');}return rows;
}
</script>
</html>