Why lifting state is needed in React - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a state variable in a React functional component.

React

const [count, [1]] = useState(0);

Drag options to blanks, or click blank then click option'

AupdateCount

BsetCount

CcountSet

DchangeCount

Attempts:

3 left

💡 Hint

Common Mistakes

Using a setter name that doesn't start with 'set'.

Mixing up the order of the array destructuring.

In React, the convention is to name the setter function as set plus the state variable name. Here, setCount is the correct setter for count.

2fill in blank

medium

Complete the code to lift the state up by passing the state setter as a prop.

React

<ChildComponent onChange=[1] />

Drag options to blanks, or click blank then click option'

AsetCount

BuseState

Ccount

DhandleChange

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the state variable instead of the setter function.

Passing a function name that is not defined.

To lift state up, you pass the setter function setCount to the child component so it can update the parent's state.

3fill in blank

hard

Fix the error in the code by choosing the correct way to update the lifted state in the child component.

React

function Child({ onChange }) {
  return <button onClick={() => [1](prev => prev + 1)}>Increment</button>;
}

Drag options to blanks, or click blank then click option'

AsetCount

Bcount

ConChange

DhandleChange

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'setCount' directly in the child when it's not in scope.

Trying to update the state variable instead of calling the setter.

The child component receives the setter function as onChange. To update the state, call onChange with the new value or updater function.

4fill in blank

hard

Fill both blanks to correctly lift state up and pass the current state as a prop.

React

function Parent() {
  const [value, [1]] = useState('');
  return <Child value=[2] onChange={setValue} />;
}

Drag options to blanks, or click blank then click option'

AsetValue

Bvalue

CsetVal

Dval

Attempts:

3 left

💡 Hint

Common Mistakes

Using inconsistent names for state and setter.

Passing the setter as the current value or vice versa.

The setter function is named 'setValue' and the current state is 'value'. Both must be used correctly to lift state and pass it down.

5fill in blank

hard

Fill all three blanks to complete a lifted state example with a controlled input.

React

function Parent() {
  const [text, [1]] = useState('');
  return <Child inputValue=[2] onInputChange=[3] />;
}

function Child({ inputValue, onInputChange }) {
  return <input value={inputValue} onChange={e => onInputChange(e.target.value)} />;
}

Drag options to blanks, or click blank then click option'

AsetText

Btext

DhandleChange

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names for the setter in parent and child.

Not passing the setter function to the child.

The state setter is 'setText', the current state is 'text', and the setter is passed as 'onInputChange' to update the state from the child.

Practice

1. Why do we lift state up in React?
lifting state means moving state to a common parent component. What is the main reason for this?

easy

A. To improve the styling of components

B. To share the same state between multiple child components

C. To avoid using props in child components

D. To make each child component have its own separate state

Solution

1. Step 1: Understand what lifting state means

   Lifting state means moving state from child components to their common parent.

2. Step 2: Identify the purpose of lifting state

   This is done so multiple children can share and update the same state, keeping data consistent.

3. Final Answer:

   To share the same state between multiple child components -> Option B

4. Quick Check:

   Sharing state = lifting state [OK]

Hint: Lifting state shares data between siblings via parent [OK]

Common Mistakes:

• Thinking lifting state is for styling
• Believing lifting state means separate states
• Confusing lifting state with removing props

2. Which of the following is the correct way to lift state up in React?

easy

A. Use global variables instead of React state

B. Keep the state inside each child component separately

C. Move the state to the nearest common parent and pass it down as props

D. Remove state and use only static values

Solution

1. Step 1: Recall the pattern of lifting state

   State should be moved to the nearest common parent component to share it.

2. Step 2: Check the options for correct syntax

   Passing state down as props from the parent is the correct React pattern.

3. Final Answer:

   Move the state to the nearest common parent and pass it down as props -> Option C

4. Quick Check:

   Lift state = parent state + props down [OK]

Hint: Lift state to parent, pass as props down [OK]

Common Mistakes:

• Keeping state only in children
• Using global variables instead of React state
• Removing state completely

3. Consider this React code snippet:

function Parent() {
  const [count, setCount] = React.useState(0);
  return (
    <>
      
      
    </>
  );
}

function ChildA({ count }) {
  return <div>Count: {count}</div>;
}

function ChildB({ setCount }) {
  return <button onClick={() => setCount(c => c + 1)}>Increment</button>;
}

What will happen when the button in ChildB is clicked?

medium

A. Nothing will change because state is not shared

B. The button will disappear

C. An error will occur because setCount is not passed correctly

D. The count displayed in ChildA will increase by 1

Solution

1. Step 1: Understand state lifting in the code

   The state count is in Parent and passed down to ChildA and ChildB.

2. Step 2: Analyze what happens on button click

   Clicking button calls setCount which updates count in Parent, causing ChildA to re-render with new count.

3. Final Answer:

   The count displayed in ChildA will increase by 1 -> Option D

4. Quick Check:

   Shared state update re-renders children [OK]

Hint: State in parent updates all children using it [OK]

Common Mistakes:

• Thinking state is local to ChildB only
• Assuming no re-render happens on state change
• Confusing props with state setters

4. You have two sibling components that need to share a counter state. You put the state inside one sibling and try to pass it to the other directly. Why is this a problem?

medium

A. Because siblings cannot directly share state; state must be lifted to their parent

B. Because React does not allow state in functional components

C. Because state can only be stored in global variables

D. Because props cannot be passed between siblings

Solution

1. Step 1: Understand React state sharing rules

   State lives inside a component and cannot be directly shared between sibling components.

2. Step 2: Identify correct sharing method

   To share state, it must be lifted to the nearest common parent, which passes it down as props.

3. Final Answer:

   Because siblings cannot directly share state; state must be lifted to their parent -> Option A

4. Quick Check:

   Siblings share state via parent [OK]

Hint: Siblings share state only via parent component [OK]

Common Mistakes:

• Thinking siblings can share state directly
• Believing React forbids state in functional components
• Confusing props passing between siblings

5. You have three components: Grandparent, Parent, and two siblings Child1 and Child2. Both children need to update and display the same piece of state. Where should you lift the state to and why?

hard

A. Lift the state to Parent because it is the nearest common ancestor of the children

B. Lift the state to Grandparent to make it global for all components

C. Keep the state inside Child1 and pass it to Child2 directly

D. Create separate states in both children and sync them manually

Solution

1. Step 1: Identify the nearest common ancestor of the siblings

   The siblings Child1 and Child2 share the Parent component as their closest common parent.

2. Step 2: Decide where to lift state for sharing

   Lifting state to Parent allows both children to access and update the same state easily without unnecessary complexity.

3. Final Answer:

   Lift the state to Parent because it is the nearest common ancestor of the children -> Option A

4. Quick Check:

   Lift state to nearest common parent [OK]

Hint: Lift state to nearest common parent of siblings [OK]

Common Mistakes:

• Lifting state too high unnecessarily
• Trying to share state directly between siblings
• Duplicating state in multiple components