"reference" in javascript?

Question

I have a set of variables that I use to tell if an question in a survey has been answered, and they are initially set to false: q0=false; q1=false; qX=false;. Then in the body, I have several input type="radio"s with .change(function(){ counter_radio(q#,INPUT'S_ID); }); binded to each. This is the code for function counter_radio():

function counter_radio(q,id){
    if (q===false) {
        q=true;
        count++;
        $("#counter").css("width", count);
        $("#percent").text(count + "%");
    }
    $("span#"+id).append(", "+q);
    $("span#"+id).fadeIn();
}

I expect that the counter to only increment once (the first time a radio from a set is selected). However, the counter is incrementing every time the input type=radio changes. My problem is that, q returns true, but q# remains false. In php, I would make q a reference to q# so when q is set to true, q# is also set to true. Is there such a construct in javascript?

david · Accepted Answer · 2011-11-01 21:16:02Z

3

You could change your bound function to:

.change(function(){ q# = counter_radio(q#,INPUT'S_ID); });

and add a return q; to the end of your counter_radio function.

answered Nov 1, 2011 at 21:16

david

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4 Comments

Jakob Jingleheimer Over a year ago

Thanks! it works (but it's not as clean as a simple function call).

david Over a year ago

If you want 'clean' then you really should refactor the whole thing to not use q1-q9 as your variable names :P

Svend Over a year ago

This functional approach is IMO far more elegant then the other suggested global object reference.

david Over a year ago

@jacob I'd create a 'Quiz' class, which would handle the count and percent information. I would then create a 'Question' class, subclass it to get the multi-choice specific questions, and store those in an array inside a Quiz object.

jfriend00 · Accepted Answer · 2011-11-01 22:05:01Z

As others have said, simple variables like booleans are passed by value, not by reference in Javascript so there is no way to change that.

If you have multiple variables like this:

var q0=false, q1=false, qX=false;

then, it might be easier to put them in an array:

var qArray = [false, false, false];

Then, because arrays and objects are passed in a way that you can modify the original, you can pass the array and an index to your function like this and you are then able to modify the original data from your function:

function counter_radio(q, index, id){
    if (q[index] === false) {
        q[index] = true;
        count++;
        $("#counter").css("width", count);
        $("#percent").text(count + "%");
    }
    $("span#"+id).append(", " + q[index]);
    $("span#"+id).fadeIn();
}

counter_radio(qArray, 2, id);

thejh · Accepted Answer · 2011-11-01 21:15:41Z

1

There's no native syntax for that, but you can e.g. use objects for that:

function counter_radio(q_,id){
    if (q_.ref===false) {
        q_.ref=true;
        count++;
        $("#counter").css("width", count);
        $("#percent").text(count + "%");
    }
    $("span#"+id).append(", "+q);
    $("span#"+id).fadeIn();
}

answered Nov 1, 2011 at 21:15

thejh

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1 Comment

Jakob Jingleheimer Over a year ago

oooow yes! except now count doesn't increment :/

kevin cline · Accepted Answer · 2011-11-01 21:50:17Z

0

I would collect the values when the user submits the form:

jQuery('radio[name=...]:checked').val()

If you want to warn the user that not all questions have been answered, use the jQuery validation plugin.

answered Nov 1, 2011 at 21:50

kevin cline

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