jQuery - create element if doesn't exist - a shorter way

How can I find out if a certain element has another element as a child? And if it doesn't, append a new one t开发者_Go百科o it and then return it.

I tried it with:

var myel = ($('> div.my', this).length > 0)
    ? $('> div.my', this)
    : $(this).append('<div class="my"></div>').css('opacity', 0);

but even though it creates my element if it doesn't exist, it doesn't return it...

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How about this?

var myel = $('> div.my', this).length ? $('> div.my', this) : $('<div class="my"></div>').css('opacity', 0).appendTo(this);

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This is how I would do it:

var myDivs = $('div.container').children('div.my');
if(myDivs.length === 0){
    myDivs = $('<div class="my"></div>   ')
        .appendTo('div.container')
        .css('opacity', 0);     
}

My reasoning is that you only need to query the children once, so if there is a lot of children, this will save some time.

Also, if there is no children, then you create one, appendTo the container, perform css and then return it.

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Similar to Alastair's method, but using filters:

$('div.outerDiv:not(:has(div.my))').each(function(){
  $('<div class="my"></div>')
    .appendTo(this)
    .css('opacity', 0);
});

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Late I know, but a different approach, adding syntactic sugar and making things legible IMO:

function ifNotExists($x){
    if(!$x || $x.length === 0) return { create : function(newX){ return newX; }}
    else return { create : function(){ return $x } };
}

//usage:
$someDiv.append(ifNotExists("div.child").create("<div class='child'>"));