What are the possible ways of updating objects in state?
Interviewer Expectations for this Question
01
Core Competency
Assesses fundamental understanding of React conventions, runtime behavior, and memory/performance considerations.
02
Evaluation Criteria
Hiring managers look for precision, avoidance of ambiguous jargon, and ability to explain trade-offs under real production conditions.
Comprehensive Model Answer
Verified Solution
- Calling
setState()with an object to merge with state:
- Using
Object.assign()to create a copy of the object:
const user = Object.assign({}, this.state.user, { age: 42 });
this.setState({ user });
- Using _spread operator_:
const user = { ...this.state.user, age: 42 };
this.setState({ user });
- Calling
setState()with a function:
this.setState((prevState) => ({
user: {
...prevState.user,
age: 42,
},
}));
Candidate Response Strategy & Interview Tips
- Start with a concise one-sentence summary: Deliver a direct, confident answer first before expanding into nuances.
- Demonstrate real-world trade-offs: Discuss where this approach excels and when you would avoid it in production systems.
- Discuss complexity & edge cases: Proactively explain time/space complexity or boundary conditions (null values, scale limits).
- Prepare for interviewer follow-ups: Technical hiring panels frequently probe deeper into concurrency, backward compatibility, or alternative libraries.