如何检查传递给javascript函数的参数值是否为空？

Question

I have the following javascript code:

    function changeButtonState(targetSelector, action, iconClass) {
        var $target = $(targetSelector);
        var $targetSpan = $(targetSelector + ' span');
        $targetSpan.removeClass('sprite-blank').addClass(iconClass);

How can I make it so that the $targetSpan.removeClass(..).addClass only work if the iconClass has a value when the function is called. I guess what I am confused about is do I check if it is defined or do I check if it has a length of 0 or more?

Answer 1

It would be best if you check for undefined as well.

function changeButtonState(targetSelector, action, iconClass) {    
    var $target = $(targetSelector);
    if (typeof iconClass !== "undefined" && iconClass) {
        var $targetSpan = $(targetSelector + ' span');
        $targetSpan.removeClass('sprite-blank').addClass(iconClass);
    }
}​

Update Even though this is a very old answer, it is still relevant. Therefore, i would like to update my answer with an improved one based on @jeremy's comment.

function changeButtonState(targetSelector, action, iconClass) {    
    var $target = $(targetSelector);
    //this will not throw exception since iconClass is implicitly declared through the input parameter 
    if (iconClass) {
        var $targetSpan = $(targetSelector + ' span');
        $targetSpan.removeClass('sprite-blank').addClass(iconClass);
    }
}​

Answer 2

This would allow the user (most likely you) to specify whether or not you want it to be active by either giving it a falsey value or a truthy value. You may also want to check if it's undefined by using the typeof operator.

if(iconClass) {
    $targetSpan.removeClass('sprite-blank').addClass(iconClass);
}