Q:

How to prevent file saving if file exists before in multer

I am using multer with NetsJs, and storing the file like below 
    @Post('upload')
    @UseInterceptors(FileInterceptor('file', {
        storage: diskStorage({
            destination: '\\nasmnt\\gtwac\\file_upload',
            filename: (req, file, callback) => {
                callback(null, file.originalname);
            },
        }),
    }),
    )
    uploadFile(@UploadedFile() file, @Query() dialer: DialerListType): void {
        console.log(JSON.stringify(dialer));
        console.log(file);

    }

When I upload same file again it will overwrite the old file, in my case I need to throw error if file already exists. How can I do that?
p.s I am new to multer

A:

In case somebody else has same problem
import { MulterModule } from '@nestjs/platform-express';
import * as fs from 'fs';
import { diskStorage } from 'multer';
import * as path from 'path';
...
     MulterModule.registerAsync({
            imports: [SharedModule],
            useFactory: async (configService: ConfigService) => ({
                storage: diskStorage({
                    destination: configService.config.dialerFilePath.upload,
                    filename: (req, file, callback) => {
                        callback(null, file.originalname);
                    },
                }),
                fileFilter: (req, file, callback) => {

                    if (fs.existsSync(path.join(configService.config.dialerFilePath.upload, file.originalname))) {
                        callback(new NotAcceptableException(`File ${file.originalname} is already uploaded!`));
                    } else {
                        callback(null, true);
                    }
                },
            }),
            inject: [ConfigService],
        }),

