I have found if ($(selector).length) {} to be insufficient. It will silently break your app when selector is an empty object {}.

var $target = $({});        
console.log($target, $target.length);

// Console output:
// -------------------------------------
// [▼ Object              ] 1
//    ► __proto__: Object

My only suggestion is to perform an additional check for {}.

if ($.isEmptyObject(selector) || !$(selector).length) {
    throw new Error('Unable to work with the given selector.');
}

I'm still looking for a better solution though as this one is a bit heavy.

I have found if ($(selector).length) {} to be insufficient. It will silently break your app when selector is an empty object {}.

var $target = $({});        
console.log($target, $target.length);

// Console output:
// -------------------------------------
// [▼ Object              ] 1
//    ► __proto__: Object

My only suggestion is to perform an additional check for {}.

if ($.isEmptyObject(selector) || !$(selector).length) {
    throw new Error('Unable to work with the given selector.');
}

I'm still looking for a better solution though as this one is a bit heavy.

Edit: WARNING! This doesn't work in IE when selector is a string.

$.isEmptyObject('hello') // FALSE in Chrome and TRUE in IE