jquery - Enable submit button only when all fields are filled

Question

In my form, I want to enable form only when all fields (and radio button list) has been selected.

So far, I have successfully made the submit button enable when the title field has content with:

onkeyup="if(this.textLength != 0) {subnewtopic.disabled = false} else {subnewtopic.disabled = true}"

My aim is to enable submit button only once everything has been filled. How do I do this?

Here is my full code with working jsfiddle:

            <form action="" method="post" id="subnewtopicform" />

                Title:
                <input type="text" name="title" onkeyup="if(this.textLength != 0) {subnewtopic.disabled = false} else {subnewtopic.disabled = true}">

<br/>

                Description:
                <textarea name="description"></textarea> 

<br/>
                Category:
<ul class="list:category categorychecklist form-no-clear" id="categorychecklist">

<li id="category-19"><label class="selectit"><input type="radio" id="in-category-19" name="category" value="19"> Animation</label></li>

<li id="category-20"><label class="selectit"><input type="radio" id="in-category-20" name="category" value="20"> Anime</label></li>

    </ul>

                <input type="submit" value="Submit Topic" class="button-primary" name="subnewtopic" id="subnewtopic" disabled="disabled" /> 

            </form>

Answer 1

Here is a fiddle for you. http://jsfiddle.net/soyn0xag/6/

$("input[type='text'], textarea").on("keyup", function(){
    if($(this).val() != "" && $("textarea").val() != "" && $("input[name='category']").is(":checked") == true){
        $("input[type='submit']").removeAttr("disabled");
    } else {
        $("input[type='submit']").attr("disabled", "disabled");
    }
});

$("input[name='category']").on("change", function(){
    if($(this).val() != "" && $("textarea").val() != "" && $("input[name='category']").is(":checked") == true){
        $("input[type='submit']").removeAttr("disabled");
    } else {
        $("input[type='submit']").attr("disabled", "disabled");
    }
});