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JavaScript Build an Interactive Website Form Validation and Manipulation Modifying Attributes

Nthulane Makgato
PLUS
Nthulane Makgato
Courses Plus Student 19,602 Points

Modifying Attributes in JQuery video

I have just watched a video on modifying attributes but there are certain lines of code that I don't understand.

                    var $submit = $(".submit input");
        function requiredFilledIn(){
            if(true) $submit.attr("disabled","disabled");
            else $submit.removeAttr("disabled");
                    }

                    $("#form span").hide();
        $("input,textarea").focus(function(){
            $(this).next().fadeIn("slow");
        }).blur(function(){
            $(this).next().fadeOut("slow");
        }).keyup(function(){
            //Check all required fields.
            requiredFilledIn();
        });

        $("#email").keyup(function(){
             //check for a valid email.
             if(false) $(this).next().removeClass("error")addClass("valid");
             else $(this).next().removeClass("valid").addClass("error");
        });

        requiredFilledIn();

So the if/else statements in the requiredFilledIn function determine whether the ".submit input" is submitted but they are determined by whether there are inputs in the ".submit input" fields. My question is, how does the "requiredFilledIn()" know that the input fields are empty or filled?

I hope that the extract of code that I gave you is enough. Thanks for your help.