在将图像加载到页面上之前，如何使用jQuery计算图像的宽度和高度？

Question

I'm banging my head against the wall on this because I know I've done it before. But this code won't work. Now, I know a lot of this is a mess because I'm trying to throw it together quickly (Make it work, make it right, make it fast, etc), but what about this is causing me so much pain and agony?

I have the following basic HTML:

<div class="js-gallery force js-on">
  <h5>More Images &raquo;</h5>
  <a href="http://url/to/image1.jpg"><img src="http://url/to/image_thumb1.jpg" alt=""></a>
  <a href="http://url/to/image2.jpg"><img src="http://url/to/image_thumb2.jpg" alt=""></a>
  <a href="http://url/to/image3.jpg"><img src="http://url/to/image_thumb3.jpg" alt=""></a>
        etc...
</div>

And the following JS to intercept link clicks, create an object to maintain state through the mini gallery (next, previous, active, etc.), and calculate screen width/height so the image fits well. Should be SO simple:

// Set up intialized variables
var overlay = $("<div class='gallery-overlay' id='gallery-overlay'></div>").hide().appendTo("body"),
  state = {},
  galleryNext = $("<a class='gallery-next' href='#'>Next</a>"),
  galleryPrev = $("<a class='gallery-prev' href='#'>Previous</a>"),
  gallery = $(".js-gallery");

gallery.addClass("js-on");

gallery.find("a").click( function (e) {
  e.preventDefault();
  state.gallery = $(this).parent(".js-gallery");
  thisHref = this.href;
  overlay.fadeIn( 200, function () { 
    buildGalleryOverlay( thisHref ); 
  });
  return false;
});

$("#gallery-overlay").live( "click", function (e) {
  overlay.fadeOut();
  overlay.find("#image-box").remove();
});

$("#image-box a").live( "click", function (e) {
  var imageBox = $("#image-box");
  imageBox.fadeOut().remove();
  buildGalleryOverlay( this.href );
  return false;
});

function buildGalleryOverlay( clickedHref ) {
  var ww = $(window).width(),
    wh = $(window).height(),
    imageBox = $("<div class='image-box' id='image-box'></div>").appendTo(overlay).show(),
    image = $("<img src='" + clickedHref + "' />"),
    iw, oldW,
    ih, oldH,
    overWidth, overHeight,
    allImages;

  window.console.log( imageBox );

  if ( !state.total ) {
    state.total = 0;
    state.images = [];
    allImages = $(state.gallery).find("a");
    $.each( allImages, function (index, value) {
      state.total += 1;
      state.images.push(value.href);
    });
  }

  state.active = state.images.indexOf( clickedHref );
  state.next = state.images[state.active + 1];
  state.prev = state.images[state.active - 1];

  image.appendTo(imageBox);
  window.console.log( image );
  iw = $(image).width();
  ih = $(image).height();

  // continued...

Right here is where the problem happens, because every so often a click on an image link will return 0 and 0 for the width and height. No idea why. And when that happens, the script doesn't work (the image gets hidden if the CSS is set to width: 0 , height: 0 —or if I turn that off then these images are too big for the screen):

  window.console.log( iw );
  window.console.log( ih );

  overWidth = iw - ww;
  overHeight = ih - wh;

  if ( overWidth > 0 || overHeight > 0 ) {
    if ( overWidth > overHeight ) {
      // Landscape
      oldW = iw;
      iw = ww - 80;
      ih = (iw * ih) / oldW;
    }
    else {
      // Portrait
      oldH = ih;
      ih = wh - 160;
      iw = (ih * iw) / oldH;
    }
  }

  galleryPrev = galleryPrev || $("<a href='##' class='gallery-prev'>Previous</a>");
  galleryNext = galleryNext || $("<a href='##' class='gallery-next'>Next</a>");

  galleryPrev.attr( "href", (state.prev || state.images[state.images.length - 1]) ).appendTo( imageBox );
  galleryNext.attr( "href", (state.next || state.images[0]) ).appendTo( imageBox );


  // Here I've turned off the CSS adjustments because iw and ih were getting 0s

  if ( iw && iw > 0 && ih && ih > 0 ) {
    image.css({width: iw + "px", height: ih + "px"});
    imageBox.css({width: iw + "px", height: ih + "px"});
  }

}

});

Answer 1

Take a look at: http://www.javascriptkit.com/jsref/image.shtml

You can't calculate the size of an image that hasn't been loaded from the server, but you can load the image via JS using the Image() object and get the calculations you need done before actually inserting that image into the page.

Answer 2

Personally, I would make a PHP script using GD that grabs the dimensions of an image residing on the server and just call it via some AJAX method that returns the results to your JavaScript. Page then never loads the image, which could be beneficial in certain situations where you may need to exclude/modify the image because of it's width/height.

Just a thought.