How do you upload an image file to mongoose database using mean js

You have plenty ways and tools to achieve what you want. I put one of them here:

For this one I use angular-file-upload as client side. So you need this one in your controller:

        $scope.onFileSelect = function(image) {
            if (angular.isArray(image)) {
                image = image[0];
            }

            // This is how I handle file types in client side
            if (image.type !== 'image/png' && image.type !== 'image/jpeg') {
                alert('Only PNG and JPEG are accepted.');
                return;
            }

            $scope.uploadInProgress = true;
            $scope.uploadProgress = 0;

            $scope.upload = $upload.upload({
                url: '/upload/image',
                method: 'POST',
                file: image
            }).progress(function(event) {
                $scope.uploadProgress = Math.floor(event.loaded / event.total);
                $scope.$apply();
            }).success(function(data, status, headers, config) {
                $scope.uploadInProgress = false;
                // If you need uploaded file immediately 
                $scope.uploadedImage = JSON.parse(data);      
            }).error(function(err) {
                $scope.uploadInProgress = false;
                console.log('Error uploading file: ' + err.message || err);
            });
        };

And following code in your view (I also added file type handler for modern browsers):

Upload image <input type="file" data-ng-file-select="onFileSelect($files)" accept="image/png, image/jpeg">
<span data-ng-if="uploadInProgress">Upload progress: {{ uploadProgress }}</span>
<img data-ng-src="uploadedImage" data-ng-if="uploadedImage">

For server side, I used node-multiparty.

And this is what you need in your server side route:

app.route('/upload/image')
    .post(upload.postImage);

And in server side controller:

var uuid = require('node-uuid'),
    multiparty = require('multiparty'),
    fs = require('fs');

exports.postImage = function(req, res) {
    var form = new multiparty.Form();
    form.parse(req, function(err, fields, files) {
        var file = files.file[0];
        var contentType = file.headers['content-type'];
        var tmpPath = file.path;
        var extIndex = tmpPath.lastIndexOf('.');
        var extension = (extIndex < 0) ? '' : tmpPath.substr(extIndex);
        // uuid is for generating unique filenames. 
        var fileName = uuid.v4() + extension;
        var destPath = 'path/to/where/you/want/to/store/your/files/' + fileName;

        // Server side file type checker.
        if (contentType !== 'image/png' && contentType !== 'image/jpeg') {
            fs.unlink(tmpPath);
            return res.status(400).send('Unsupported file type.');
        }

        fs.rename(tmpPath, destPath, function(err) {
            if (err) {
                return res.status(400).send('Image is not saved:');
            }
            return res.json(destPath);
        });
    });
};

As you can see, I store uploaded files in file system, so I just used node-uuid to give them unique name. If you want to store your files directly in database, you don't need uuid, and in that case, just use Buffer data type. Also please take care of things like adding angularFileUpload to your angular module dependencies.

I got ENOENT and EXDEV errors. After solving these, below code worked for me.

var uuid = require('node-uuid'),
multiparty = require('multiparty'),
fs = require('fs');

var form = new multiparty.Form();
form.parse(req, function(err, fields, files) {
    var file = files.file[0];
    var contentType = file.headers['content-type'];
    var tmpPath = file.path;
    var extIndex = tmpPath.lastIndexOf('.');
    var extension = (extIndex < 0) ? '' : tmpPath.substr(extIndex);
    // uuid is for generating unique filenames.
    var fileName = uuid.v4() + extension;
    var destPath = appRoot +'/../public/images/profile_images/' + fileName;

    // Server side file type checker.
    if (contentType !== 'image/png' && contentType !== 'image/jpeg') {
        fs.unlink(tmpPath);
        return res.status(400).send('Unsupported file type.');
    }

    var is = fs.createReadStream(tmpPath);
    var os = fs.createWriteStream(destPath);

    if(is.pipe(os)) {
        fs.unlink(tmpPath, function (err) { //To unlink the file from temp path after copy
            if (err) {
                console.log(err);
            }
        });
        return res.json(destPath);
    }else
        return res.json('File not uploaded');
});

for variable 'appRoot' do below in express.js

path = require('path');
global.appRoot = path.resolve(__dirname);