<input class="form-control" type="text" id="username" name="username" placeholder="" value="初始值" onblur="keyblurfun()">
<input class="form-control" type="text" id="username" name="username" placeholder="" value="{{ user.get('userid','') }}">
<script>
    var username = $("#username").val();   // 获取 id 为 username 的标签的值。
    console.log(username);
    $("#username").val("hello world");     // 设置 id 为 username 的标签的值
    console.log($("#username").val());
</script>

<textarea class="form-control" id="brief" name="brief" cols=10 rows=6 placeholder="">Java</textarea>
<textarea class="form-control" id="brief" name="brief" cols=10 rows=6 placeholder="">{{study.get('brief','')}}</textarea>
<script>
    var content= $("#brief").val();          // 获取 textarea 标签的值     
    console.log(content);            // Java
    $("#brief").val("Python");               // 设置 textarea 标签的值 
    console.log($("#brief").val());  // Python
</script>