js - form提交action之前用js操作

在提交action之前先用js操作一下，若果为false则不执行action：

html：

<form name="launch" method="post" onsubmit="return launchTopic();" action="/sns/launch.html"><textarea class="txd-comment" rows="5" name="content" id="launchTopicContent"></textarea><input type="hidden" name="circle" value="${id}"><div class="row"><span class="textbutton"><input type="submit" name="submit_btn" value="发起话题"></span></div></form>

js：

                     <script type="text/javascript">        function launchTopic(){        if(!isLogin()){        return false;        }        var content = document.getElementById('launchTopicContent').value;        if(content == null || content.trim().length == 0){        alert("请输入内容");        return false;        }        return true;             }