<textarea style="width:100%;height:150px;" id="content">
     要下载的文本内容。。。。
</textarea>

<a download="data.txt" id="save-btn" @click="file"><button type="button">下载</button></a>
var content, saveBtn;

	        content = document.querySelector( '#content' );
	        saveBtn = document.querySelector( '#save-btn' );
	        content.addEventListener( 'change', function self(){
	            saveBtn.setAttribute( 'href', 'data:text/paint; utf-8,' + content.value );
	            return self;
	        }() );