Which of the following is the correct syntax to update component state using setState?

Which of the following is the correct syntax to update component state using setState?

• A. this.setState( { someKey: newValue} );
• B. this.updateState( { someKey: newValue} );
• C. this.changeState( { someKey: newValue} );
• D. setState( { someKey: newValue} );

Answer: (A)

In React class components, updating state is done with the component’s setState method, using this.setState in order for React to schedule a re-render. The correct approach passes an object with the keys to update, for example this.setState({ someKey: newValue }), which merges that change into the current state. This is the standard pattern because setState is a method on the component instance, and calling it with an object updates only the specified keys while preserving the rest of the state. It also handles the update asynchronously as part of React’s rendering cycle. The other forms try to call methods that don’t exist on a component (like updateState or changeState) or omit the this. prefix (setState without this), which would not correctly reference the component’s method and won’t trigger React’s state management or rendering.

In React class components, updating state is done with the component’s setState method, using this.setState in order for React to schedule a re-render. The correct approach passes an object with the keys to update, for example this.setState({ someKey: newValue }), which merges that change into the current state.

This is the standard pattern because setState is a method on the component instance, and calling it with an object updates only the specified keys while preserving the rest of the state. It also handles the update asynchronously as part of React’s rendering cycle.

The other forms try to call methods that don’t exist on a component (like updateState or changeState) or omit the this. prefix (setState without this), which would not correctly reference the component’s method and won’t trigger React’s state management or rendering.