file_upload.js

// directly uploads to S3

// See http://philfreo.com/blog/how-to-allow-direct-file-uploads-from-javascript-to-amazon-s3-signed-by-python/
// See https://github.com/elasticsales/s3upload-coffee-javascript

editors.Filepicker = editors.Text.extend({
        tagName: 'div',

        events: {
            'change input[type=file]': 'uploadFile',
            'click .remove': 'removeFile'
        },

        initialize: function(options) {
            _.bindAll(this, 'filepickerSuccess', 'filepickerError', 'filepickerProgress');
            editors.Text.prototype.initialize.call(this, options);
            this.$input = $('<input type="hidden" name="'+this.key+'" />');
            this.$uploadInput = $('<input type="file" multiple="multiple" />');
            this.$loader = $('<p class="upload-status"><span class="loader"></span> Uploading&hellip;</p>');
            this.$error = $('<p class="upload-error error">Error</p>');
            this.$list = $('<ul class="file-list">');
        },

        // return an array of file dicts
        getValue: function() {
            var val = this.$input.val();
            return val ? JSON.parse(val) : [];
        },

        setValue: function(value) {
            var str, files = value;
            if (_(value).isObject()) {
                str = JSON.stringify(value);
            } else {
                files = value ? JSON.parse(value) : [];
            }
            this.$input.val(str);
            this.updateList(files);
        },

        render: function(options) {
            editors.Text.prototype.render.apply(this, arguments);

            this.$el.append(this.$input);
            this.$el.append(this.$uploadInput);
            this.$el.append(this.$loader.hide());
            this.$el.append(this.$error.hide());
            this.$el.append(this.$list);
            return this;
        },

        uploadFile: function() {
            var s3upload = new S3Upload({
                file_dom_selector: this.$uploadInput,
                s3_sign_put_url: '/sign_s3_put/',
                onProgress: this.filepickerProgress,
                onFinishS3Put: this.filepickerSuccess,
                onError: this.filepickerError
            });
        },

        filepickerSuccess: function(s3Url, file) {
            console.log('File uploaded', s3Url);
            this.$loader.hide();
            this.$error.hide();
            this.$uploadInput.val('');

            var newFiles = [{
                url: s3Url,
                filename: file.name,
                size: file.size,
                content_type: file.type
            }];

            console.log('File uploaded (processed)', newFiles);
            this.setValue(this.getValue().concat(newFiles));
        },

        filepickerError: function(msg, file) {
            console.debug('Filepicker error', msg);
            this.$loader.hide();
            this.$error.show();
        },

        filepickerProgress: function(percent, message, publicUrl, file) {
            //console.log('Filepicker progress', percent, message);
            this.$loader.show();
            this.$error.hide();
        },

        updateList: function(files) {
            // this code is currently duplicated as a handlebar helper (I wanted to let this
            // backbone-forms field stand on its own)
            var displayFilesize = function(bytes) {
                // TODO improve this function
                return Math.floor(bytes / 1024) + 'K';
            };

            this.$list.empty();
            _(files).each(function(file) {
                var a = $('<a>', {
                    target: '_blank',
                    href: file.url,
                    text: file.filename + ' (' + file.content_type + ') ' + displayFilesize(file.size)
                });
                var li = $('<li>').append(a);
                li.append(a, ' ', $('<a href="#" class="remove"><i class="icon-remove"></i></a>').data('url', file.url));
                this.$list.append(li);
            }, this);

            this.$list[files.length ? 'show' : 'hide']();
        },

        removeFile: function(ev) {
            if (ev) ev.preventDefault();
            var url = $(ev.currentTarget).data('url');
            var files = this.getValue();
            this.setValue(_(files).reject(function(one) {
                return one.url === url;
            }));
        }

    });

using_filepickerio.js

// this version uses the filepicker.io service

editors.FilepickerIO = editors.Text.extend({
        tagName: 'div',

        events: {
            'change input[type=file]': 'uploadFile',
            'click .remove': 'removeFile'
        },

        initialize: function(options) {
            _.bindAll(this, 'filepickerSuccess', 'filepickerError', 'filepickerProgress');
            editors.Text.prototype.initialize.call(this, options);
            this.$input = $('<input type="hidden" name="'+this.key+'" />');
            this.$uploadInput = $('<input type="file" multiple="multiple" />');
            this.$loader = $('<p class="upload-status"><span class="loader"></span> Uploading&hellip;</p>');
            this.$error = $('<p class="upload-error error">Error</p>');
            this.$list = $('<ul class="file-list">');
        },

        // return an array of file dicts
        getValue: function() {
            var val = this.$input.val();
            return val ? JSON.parse(val) : [];
        },

        setValue: function(value) {
            var str, files = value;
            if (_(value).isObject()) {
                str = JSON.stringify(value);
            } else {
                files = value ? JSON.parse(value) : [];
            }
            this.$input.val(str);
            this.updateList(files);
        },

        render: function(options) {
            editors.Text.prototype.render.apply(this, arguments);

            this.$el.append(this.$input);
            this.$el.append(this.$uploadInput);
            this.$el.append(this.$loader.hide());
            this.$el.append(this.$error.hide());
            this.$el.append(this.$list);
            return this;
        },

        uploadFile: function() {
            filepicker = require('filepicker-io');

            // https://developers.filepicker.io/docs/web/#local-upload
            filepicker.uploadFile(this.$uploadInput.get(0), this.filepickerSuccess, this.filepickerError, this.filepickerProgress);
        },

        filepickerSuccess: function(files) {
            console.log('Filepicker (raw)', files);
            this.$loader.hide();
            this.$error.hide();
            this.$uploadInput.val('');

            // when uploading one file, it returns just an object
            if (!_(files).isArray()) { files = [files]; }

            // turn response array into a flatter array of objects
            var newFiles = _(files).map(function(one) {
                return {
                    url: one.url,
                    filename: one.data.filename,
                    s3_key: one.data.key,
                    size: one.data.size,
                    content_type: one.data.type
                };
            });
            console.log('Filepicker (processed)', newFiles);
            this.setValue(this.getValue().concat(newFiles));
        },

        filepickerError: function(msg) {
            console.debug('Filepicker error', msg);
            this.$loader.hide();
            this.$error.show();
        },

        filepickerProgress: function(percent) {
            this.$loader.show();
            this.$error.hide();
        },

        updateList: function(files) {
            // this code is currently duplicated as a handlebar helper (I wanted to let this
            // backbone-forms field stand on its own)
            var displayFilesize = function(bytes) {
                // TODO improve this function
                return Math.floor(bytes / 1024) + 'K';
            };

            this.$list.empty();
            _(files).each(function(file) {
                var a = $('<a>', {
                    target: '_blank',
                    href: file.url,
                    text: file.filename + ' (' + file.content_type + ') ' + displayFilesize(file.size)
                });
                var li = $('<li>').append(a);
                li.append(a, ' ', $('<a href="#" class="remove"><i class="icon-remove"></i></a>').data('s3_key', file.s3_key));
                this.$list.append(li);
            }, this);

            this.$list[files.length ? 'show' : 'hide']();
        },

        removeFile: function(ev) {
            if (ev) ev.preventDefault();
            var s3_key = $(ev.currentTarget).data('s3_key');
            var files = this.getValue();
            this.setValue(_(files).reject(function(one) {
                return one.s3_key === s3_key;
            }));
        }

    });