Question

I have a function with 2 parameters, it should work whether a the 2nd parameter is assigned or not in the bracket. Basically, if it’s assigned then do something if not do something else or just don’t bother about it.

vf.showHide = function (trigger, target) {
    var $trigger = $(trigger),
        trigParent = $trigger.parent(),
        trigDataView = $trigger.data('view'),
        numShown = $trigger.data('showalways'),
        basketSubtotalElem = $('.subtotal .monthlyCost span.price, .subtotal .oneOffCost span.price, .subtotal label h3, .vat *');

    target = target || null; // This is the 2nd parameter but I don't know if this right...

    trigParent.delegate(trigger, 'click', function (e) {
        var elem = $(this);

        target = $(elem.attr('href'));

        e.preventDefault();

        if (trigDataView === 'showhide') {
            if($('.filterBlock')){
                if (target.is(':visible')) {
                    target.hide();
                    elem.find('span').removeClass('minus').addClass('plus');
                } else {
                    target.show();
                    elem.find('span').removeClass('plus').addClass('minus');
                }
            } 
        }
    });
}

So if the function is called like this: vf.showHide('a', 'div') it works and if it’s called with 1 parameter like this: vf.showHide('a') it’s should still works and error is thrown.

Many thanks

Answer 1

When you invoke a function, if you pass fewer parameters than expected, the parameters you omit are given the undefined value. So in your case:

vf.showHide = function(trigger, target) {
    if (target === undefined) {
        //target parameter is not passed any value or passed undefined value
        //add code to process here, e.g. assign target a default value
    }
}

target = target || null: if target is evaluated to false, it’s assigned to null. Take notice that empty string, zero number (0), NaN, undefined, null, false are evaluated to false. So please be careful to write code like that.