When working with multiple Plupload instances, a common challenge is distinguishing which specific instance triggered a file upload response. Without proper identification, it becomes difficult to process the uploaded files correctly in your application.

Here's a solution using AngularJS to track which file input initiated the upload process:

Seting Up Multiple Upload Instances

var fileUploader = new plupload.Uploader({
    browse_button: ['primary_upload', 'secondary_upload'],
    url: '/api/upload',
    flash_swf_url: 'lib/moxie.swf',
    silverlight_xap_url: 'lib/moxie.xap',
    filters: {
        max_file_size: '10mb',
        mime_types: [{
            title: "Image files",
            extensions: "jpg,png,gif,jpeg"
        }]
    },
    multi_selection: false,
    init: {
        FilesAdded: function(up, files) {
            fileUploader.start();
        },
        FileUploaded: function(up, file, info) {
            var response = JSON.parse(info.response);
            
            if ($scope.currentInputId === 'primary_upload') {
                $scope.$apply(function() {
                    $scope.primaryImages.push({
                        id: file.id,
                        src: response.data[0],
                        isDefault: !$scope.primaryImages.length
                    });
                    $scope.primaryImage = $scope.primaryImages.length > 1 ? 
                        $scope.primaryImage : response.data[0];
                });
            }
            
            if ($scope.currentInputId === 'secondary_upload') {
                $scope.$apply(function() {
                    $scope.secondaryImages.push({
                        id: file.id,
                        src: response.data[0],
                        isDefault: !$scope.secondaryImages.length
                    });
                    $scope.secondaryImage = $scope.secondaryImages.length > 1 ? 
                        $scope.secondaryImage : response.data[0];
                });
            }
        },
        Error: function(up, err) {
            alert('Upload error: ' + err.message);
        }
    }
});

HTML File Inputs with Click Tracking

<input type="file" id="primary_upload" 
       name="file" 
       class="upload-input" 
       ng-click="trackUploadInput('primary_upload')">

<input type="file" id="secondary_upload" 
       name="file" 
       class="upload-input" 
       ng-click="trackUploadInput('secondary_upload')">

AngularJS Controller Function

$scope.trackUploadInput = function(inputId) {
    $scope.currentInputId = inputId;
};

This approach allows you to track which file input was clicked before the upload completes, enabling proper handling of the response data for each specific upload instance.