查看jQuery file upload的image preview如何工作的

查看readme中的说明，

JavaScript Load Image library v. 1.13.0+: Required for the image previews and resizing functionality.
JavaScript Canvas to Blob polyfill v. 2.1.1+:Required for the image previews and resizing functionality.

注释掉这个js的引用

然后发现错误在loadImage.parseMetaData，提示loadImage undefined

loadImageMetaData: function (data, options) {
                if (options.disabled) {
                    return data;
                }
                var that = this,
                    dfd = $.Deferred();
                loadImage.parseMetaData(data.files[data.index], function (result) {
                    $.extend(data, result);
                    dfd.resolveWith(that, [data]);
                }, options);
                return dfd.promise();
            },

在loadImageMetaData函数前面，加上console.trace(); 刷新页面，再次尝试，然后查看stack trace，但是这个结果没有意义。可读性太差了。

使用stacktrace.js查看堆栈信息

引用https://cdnjs.cloudflare.com/ajax/libs/stacktrace.js/2.0.0/stacktrace.js，然后在loadImageMetaData函数处，输出堆栈信息

 var callback = function(stackframes) {
                    var stringifiedStack = stackframes.map(function(sf) {
                        return sf.toString();
                    }).join('\n');
                    console.log(stringifiedStack);
                };

                var errback = function(err) { console.log(err.message); };

                StackTrace.get().then(callback).catch(errback);

loadImageMetaData()@http://172.31.212.20:8082/jQuery-File-Upload-Demo/js/jquery.fileupload-image.js:289:28

func()@http://172.31.212.20:8082/jQuery-File-Upload-Demo/js/jquery.fileupload-process.js:84:65

_processFile: function (data, originalData) {
            var that = this,
                dfd = $.Deferred().resolveWith(that, [data]),
                chain = dfd.promise();
            this._trigger('process', null, data);
            $.each(data.processQueue, function (i, settings) {
                var func = function (data) {
                    if (originalData.errorThrown) {
                        return $.Deferred()
                                .rejectWith(that, [originalData]).promise();
                    }
                    return that.processActions[settings.action].call(
                        that,
                        data,
                        settings
                    );
                };
                chain = chain.then(func, settings.always && func);
            });
            chain
                .done(function () {
                    that._trigger('processdone', null, data);
                    that._trigger('processalways', null, data);
                })
                .fail(function () {
                    that._trigger('processfail', null, data);
                    that._trigger('processalways', null, data);
                });
            return chain;
        },

function()@http://ajax.googleapis.com/ajax/libs/jquery/1.11.3/jquery.js:3305:32

apply()@http://ajax.googleapis.com/ajax/libs/jquery/1.11.3/jquery.js:3148:29

add()@http://ajax.googleapis.com/ajax/libs/jquery/1.11.3/jquery.js:3194:6

function()@http://ajax.googleapis.com/ajax/libs/jquery/1.11.3/jquery.js:3304:28

callback.apply()@http://ajax.googleapis.com/ajax/libs/jquery/1.11.3/jquery.js:384:22

jQuery.each()@http://ajax.googleapis.com/ajax/libs/jquery/1.11.3/jquery.js:3301:13

promise.promise()@http://ajax.googleapis.com/ajax/libs/jquery/1.11.3/jquery.js:3361:8

jQuery.Deferred(function()@http://ajax.googleapis.com/ajax/libs/jquery/1.11.3/jquery.js:3300:19

_processFile/<()@http://172.31.212.20:8082/jQuery-File-Upload-Demo/js/jquery.fileupload-process.js:90:31

   chain = chain.then(func, settings.always && func);

callback.apply()@http://ajax.googleapis.com/ajax/libs/jquery/1.11.3/jquery.js:384:22

_processFile()@http://172.31.212.20:8082/jQuery-File-Upload-Demo/js/jquery.fileupload-process.js:78:15

$.each(data.processQueue, function (i, settings) {

$.widget/</proxiedPrototype[prop]</<()@http://172.31.212.20:8082/jQuery-File-Upload-Demo/js/vendor/jquery.ui.widget.js:127:25

returnValue = value.apply( this, arguments );

func()@http://172.31.212.20:8082/jQuery-File-Upload-Demo/js/jquery.fileupload-process.js:153:41

return that._processFile(opts, data);