Node-RED functions are custom JavaScript code nodes in the Node-RED flow-based visual programming tool that enable users to tackle complex data transformations, execute personalized logic, and integrate disparate components within their flows. These functions allow users to write custom JavaScript code to process and manipulate message data, making it possible to perform tasks such as data transformation, filtering, validation, conditional logic, mathematical operations, text processing, date and time manipulation, error handling, dynamic content generation, and multi-step processing. By using Node-RED functions, users can transcend the boundaries of pre-built solutions and infuse their flows with custom logic, data mastery, and creativity, ultimately empowering them to achieve more complex automation and integration projects.