In the video, a candidate participates in a live coding mock interview where they build a mini Google Sheets application using React.js, focusing on rendering labeled cells that can display numbers or the sum of referenced cells based on user input. The candidate emphasizes the importance of planning, state management, and debugging practices before coding, while also discussing performance optimization techniques like React.memo.
In the video, the presenter conducts a live coding mock interview focused on building a mini Google Sheets application using React.js. The challenge involves rendering four labeled cells (A, B, C, D), each containing a text input where users can type. The cells should display either the number entered or, if the input contains letters, the sum of the referenced cells. The interviewer emphasizes that no AI assistance is allowed during the coding process, encouraging the candidate to clarify any questions before starting.
Before diving into coding, the candidate is advised to outline the component structure and state management. They sketch a low-fidelity version of the UI, identifying that each cell will be a separate component with its own state. The candidate discusses the need to lift the state up to a parent component since the values of sibling cells (A and B) are required to compute the display value for cell C. The importance of clear communication and planning before coding is highlighted, as it helps the interviewer understand the candidate’s thought process.
The candidate is reminded to focus on dynamic components that will change based on user interaction. They discuss the implications of lifting state and the potential for unnecessary re-renders, suggesting the use of React.memo to optimize performance. The interviewer stresses the importance of balancing planning and coding time, as spending too long on wireframing could leave little time for actual implementation. The candidate is encouraged to practice this workflow to improve their coding interviews.
As the coding begins, the candidate opts for a brute-force approach by hardcoding the four cells within a single component. They initialize the state as a key-value pair, setting the initial values to zero. The candidate implements an onChange handler to update the state based on user input, demonstrating how to manage state mutations effectively. They also emphasize the importance of debugging tools to track state changes during the coding process.
Finally, the candidate addresses the requirement for cells to display the sum of referenced cells when letters are input. They create a function to compute the display value based on the cell’s value and implement logic to handle letter inputs. The presenter concludes by discussing common mistakes developers make during interviews, such as jumping straight into coding without planning, over-relying on AI, and neglecting debugging practices. They emphasize the importance of starting with a simple solution and discussing edge cases with the interviewer after the initial implementation is complete.