<form id="form">

    <input type="text" name="aaa">

    <select name="bbb">

        <option value="">请选择</option>

        <option value="1">选项1</option>

        <option value="2">选项2</option>

        <option value="3">选项3</option>

    </select>

    <button type="button" id="submit">提交</button>

</form>

//提交表单

$('#submit').click(function(){

    var data = {};

    var t = $('#form').serializeArray();

    $.each(t, function() {

        data [this.name] = this.value;

    });

    console.log(data);

    if(data.aaa == ''){alert("aaa不能为空！");return false;}

    if(data.bbb == ''){alert("bbb不能为空！");return false;}

    $('#form').submit();

});

<input type="text" name="aaa" required="required">

<select name="bbb" required="required">

    <option value="">请选择</option>

    <option value="1">选项1</option>

    <option value="2">选项2</option>

    <option value="3">选项3</option>

</select>

<button type="submit">提交</button>