Javascript太慢了吗？

I'm trying to read the size of an image and regulate its margin if its larger than 150 in height. But I'm always getting a '0' in the console when running this code:

        var coverImg;
        coverImg = document.getElementById('userCover');

        $.ajax({
                type: "POST",
                url: 'code/submit/submitGetUserData.php',
                data: {id: userID, what: 'all'},
                async: false,
                success:function(data,status){
                    var dataArray = data.split(',');

                    document.getElementById('userAvatar').src = dataArray[0];
                    coverImg.src = dataArray[1];
                    $('#userName').text(dataArray[2]);
                },
                error: function(){
                    alert("error occured");

                },
                complete: function(){
                    console.log(coverImg.height);

                    if(document.getElementById('userCover').height > 150)
                    {
                        var regulate = 0;
                        regulate = (coverImg.height - 150) / 2;
                        regulate = regulate * (-1);



                        coverImg.style.marginTop = regulate;
                    }
                }
        });

Is JS too slow to read the height property?!

I hope someone can help me!

Move the code currently placed in complete into coverImg.onload handler. For example:

coverImg.onload = function() {
   if(document.getElementById('userCover').height > 150) {
     var regulate = (150 - this.height) / 2;
     // ...
   }
}
coverImg.src = dataArray[1];

... as browser can determine the height of <img> element only after it's fully loaded - and complete callback is fired before that.