To avoid the form submition, just use required attr in the input fields.
<input type="text" required>
Or, after submit
When the form is submited, you can use str.trim() to remove white spaces form start and end of an string. I did a submit function to show you:
submitFunction(formData){
if(!formData.foo){
// launch an alert to say the user the field cannot be empty
return false;
}
else
{
formData.foo = formData.foo.trim(); // removes white
// do your logic here
return true;
}
}