Formio.js get JSON text from builder method

I read the docs about formio.js on github. But I can't see how to get json text after the form is build.

Here's my code:

<div id='builder'></div>
<script type='text/javascript'>
    var builder = Formio.builder(document.getElementById('builder'), {}, {});

    builder.then(function(form){
        form.on("change", function(e){
             console.log("Something changed on the form builder");
        });
    });
</script>

Now I want to take the json schema of the form to store in database.

try something like:

...
form.on("change", function(e){
    console.log("Something changed on the form builder");
    var jsonSchema = JSON.stringify(form.submission, null, 4);
    console.log(jsonSchema); // this is the json schema of form components
});
...

or you could try using builder.instance.schema, as ...

form.on("change", function(e){
    console.log("Something changed on the form builder");
    var jsonSchema = JSON.stringify(builder.instance.schema, null, 4);
    console.log(jsonSchema);
});
...