-----------------html

<div><textarea autoHeight="true">textarea</textarea></div>
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-----------------js

$.fn.autoHeight = function(){
    
    function autoHeight(elem){
        elem.style.height = 'auto';
        elem.scrollTop = 0; //防抖动
        elem.style.height = elem.scrollHeight + 'px';
    }
    
    this.each(function(){
        autoHeight(this);
        $(this).on('keyup', function(){
            autoHeight(this);
        });
    });
 
}
$('textarea[autoHeight]').autoHeight();
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