A JR backend developer is a professional who works on the logical, functional and data part of an application. It is responsible for creating and managing databases, servers, APIs and other components that run behind the scenes of an application. He is also responsible for ensuring the quality, security, and performance of the code.

A JR backend developer can do several tasks, such as:

- Develop, test and maintain the backend code of an application using programming languages such as Java, Python, Ruby, PHP, etc.;

- Create and manipulate relational (SQL) and non-relational (NOSQL) databases to store and retrieve data;

- Create and integrate RESTful APIs to communicate the application with external services or other system components;

- Use version control tools, such as Git, to manage source code and collaborate with other developers;

- Use automated testing and code quality tools to verify code functionality, coverage, and compliance;

- Use backend frameworks and libraries, such as Node.js, Express, Django, Rails, Laravel, etc., to facilitate development and increase productivity;

- Use agile methodologies, such as Scrum and Kanban, to organize teamwork and deliver value to the customer;

- Learn and apply emerging technologies such as cloud computing, microservices, serverless, etc., to improve application scalability, availability and efficiency.