javascriptjquerydebuggingphotoswipe

Javascript code executes correctly when debugging, but doesn't work without browser Dev Tools running


I am trying to build a simple image uploader/gallery viewer for a webpage using PhotoSwipe. The gallery viewer plugin works without issues and needs an array (items in the code below) with the image src and the width and height per image. The function readImageDimensions() gets the data and later saves it to items.

When I'm debugging the code it runs flawlessly and the gallery gets the data, but if I skip the debugger the item variable has indexed two objects, but the src, w, h all have null values. Is it something in the code that runs asynchronously or otherwise disrupt the flow when the code isn't running through the debug process?

Code for uploading and presenting the images:

var thumbsDiv = "";
var items = [];

document.addEventListener("DOMContentLoaded", init, false);

function init() {
    document.querySelector('.file-uploader').addEventListener('change', onFilesSelected, false);
    thumbsDiv = document.querySelector(".thumbs-div");
}

function onFilesSelected(e) {

    if (!e.target.files || !window.FileReader) return;

    thumbsDiv.innerHTML = "";

    var width = 0;
    var height = 0;

    items = [];

    function readImageDimensions(data) {
        var image = new Image();

        image.src = data;
        width = image.width;
        height = image.height;
    }

    var files = e.target.files;
    var filesArr = Array.prototype.slice.call(files);
    filesArr.forEach(function (f) {
        if (!f.type.match("image.*")) {
            return;
        }

        var reader = new FileReader();
        reader.onloadend = function (e) {
            var result = e.target.result;
            var html = '<div class="img-wrap"><span class="close">&times;</span><img src="' + result + '"/>' + f.name + '</div>';
            thumbsDiv.innerHTML += html;

            readImageDimensions(result);

            items.push({
                src: result,
                w: width,
                h: height
            });
        }
        reader.readAsDataURL(f);
    });

}

Code for instantiating the gallery:

var openGallery = function () {
    var pswpElement = document.querySelectorAll(".pswp")[0];

    var options = {
        index: 0
    };

    var gallery = new PhotoSwipe(pswpElement, PhotoSwipeUI_Default, items, options);
    gallery.init();
}

Solution

  • The issue was in fact that the image data was loaded asynchronously, and the program tried to read the image dimensions before it was loaded. I used HMR's comment to further research the onload() handler and modified the readImageDimensions() like this:

    function readImageDimensions(data) {
        var image = new Image();
        console.log(data);
    
        image.onload = function () {
            width = image.width;
            height = image.height;
    
            items.push({
                src: data,
                w: width,
                h: height
            });
        }
        image.src = data;
    }
    

    This way, the onload() gets "primed" with reading the width and height, and won't do that until the whole image data is loaded onto the browser cache. The code also pushes the data onto the items[] array and obviously I'll rename the method into something better, like setImageDataForGallery().