Reusable UI components in React - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a reusable UI component in React?

A reusable UI component is a piece of code that defines a part of the user interface which can be used multiple times in different places, helping to keep the code simple and consistent.

beginner

Why should we use reusable components?

Using reusable components saves time, reduces errors, and makes the app easier to maintain because you write the code once and use it many times.

beginner

How do you pass data to a reusable component in React?

You pass data to a reusable component using props, which are like parameters that customize the component's content or behavior.

intermediate

What is the difference between a functional component and a reusable component?

A functional component is a type of React component defined as a function. A reusable component is any component (often functional) designed to be used multiple times with different data.

beginner

How can you make a button component reusable for different labels and actions?

Create a button component that accepts label and onClick as props. This way, you can change the text and what happens when clicked without rewriting the button.

What is the main purpose of reusable UI components in React?

A To write code once and use it many times

B To make the app slower

C To increase the file size

D To avoid using props

Reusable components help you write code once and use it many times, making development faster and easier.

How do you customize a reusable component's content?

A By changing its internal code every time

B By copying and pasting it

C By using global variables

D By passing props to it

Props allow you to customize a component's content or behavior without changing its code.

Which React feature helps you create reusable UI parts?

A Components

B Events

C State

D Hooks

Components are the building blocks in React used to create reusable UI parts.

What type of React component is recommended for creating reusable UI components?

A Class components

B Functional components

C Inline styles

D DOM elements

Functional components are simple and recommended for creating reusable UI components in modern React.

If you want a button component to do different things when clicked, what should you pass to it?

A A different CSS file

B A new component each time

C An onClick function as a prop

D A global variable

Passing an onClick function as a prop lets the button perform different actions when clicked.

Explain what reusable UI components are and why they are useful in React.

Think about how you can use the same building block many times with different details.

Describe how you would create a reusable button component that can show different text and perform different actions.

Focus on how props help customize the button.

Practice

1. What is the main benefit of creating reusable UI components in React?

easy

A. They automatically fix bugs

B. They make the app run faster

C. They save time and keep the app consistent

D. They replace the need for CSS styling

Solution

1. Step 1: Understand the purpose of reusable components

   Reusable components are designed to be used multiple times, reducing repeated code.

2. Step 2: Identify the main benefit

   Using reusable components saves development time and keeps the app's look and behavior consistent.

3. Final Answer:

   They save time and keep the app consistent -> Option C

4. Quick Check:

   Reusable components = save time + consistency [OK]

Hint: Reusable means use again to save time and stay consistent [OK]

Common Mistakes:

• Thinking reusable components speed up app runtime
• Believing they fix bugs automatically
• Confusing styling with component reuse

2. Which of the following is the correct way to pass a prop named title with value "Hello" to a React component Card?

easy

A.

B.

C.

D.

Solution

1. Step 1: Recall JSX prop syntax

   Props are passed as attributes with name=value pairs, using quotes for strings.

2. Step 2: Check each option

   uses correct JSX syntax: title="Hello". Others have syntax errors.

3. Final Answer:

   <Card title="Hello" /> -> Option A

4. Quick Check:

   Props in JSX use name="value" [OK]

Hint: Props look like HTML attributes with quotes for strings [OK]

Common Mistakes:

• Using curly braces without variable (Option B)
• Adding extra quotes around prop name (Option C)
• Using colon instead of equals (Option A)

3. Given this React component:

function Button({ label }) {
  return <button>{label}</button>;
}

// Usage:
<Button label="Click me" />

What will be rendered on the page?

medium

A. label

B. Nothing will render

C. {label}

D. Click me

Solution

1. Step 1: Understand prop usage in the component

   The component receives label as a prop and inserts it inside the button element.

2. Step 2: Check the usage

   The component is used with label="Click me", so the button shows "Click me" text.

3. Final Answer:

   <button>Click me</button> -> Option D

4. Quick Check:

   Prop label = "Click me" shown inside button [OK]

Hint: Props passed show as content inside component tags [OK]

Common Mistakes:

• Thinking the literal word 'label' appears
• Confusing JSX expression with string
• Assuming component renders nothing without explicit return

4. What is wrong with this reusable React component code?

function Alert(props) {
  return <div>{message}</div>;
}

// Usage:
<Alert message="Warning!" />

medium

A. The variable 'message' is not defined inside the component

B. The component does not receive props correctly

C. The usage of the component is incorrect

D. The component should return a button instead of a div

Solution

1. Step 1: Check how props are used inside the component

   The component uses {message} but does not extract it from props.

2. Step 2: Identify the error

   Since message is not defined or extracted, this causes a reference error.

3. Final Answer:

   The variable 'message' is not defined inside the component -> Option A

4. Quick Check:

   Props must be accessed via props or destructuring [OK]

Hint: Always get props from function parameter before use [OK]

Common Mistakes:

• Using prop names directly without props or destructuring
• Assuming usage syntax is wrong
• Thinking component must return button

5. You want to create a reusable Input component that can show a label and accept user input. Which approach correctly allows customizing the label text and input placeholder using props?

hard

A. function Input() {
return (
<label>
label
<input placeholder="placeholder" />
</label>
);
}

B. function Input({ label, placeholder }) {
return (
<label>
{label}
<input placeholder={placeholder} />
</label>
);
}

C. function Input(props) {
return (
<label>
props.label
<input placeholder="props.placeholder" />
</label>
);
}

D. function Input({ label, placeholder }) {
return (
<label>
<input placeholder={label} />
{placeholder}
</label>
);
}

Solution

1. Step 1: Check prop usage for label and placeholder

   Props should be destructured and used inside JSX expressions with curly braces.

2. Step 2: Verify correct placement of label and placeholder

   function Input({ label, placeholder }) { return ( <label> {label} <input placeholder={placeholder} /> </label> ); } correctly places label text and uses placeholder prop inside input element.

3. Final Answer:

   function Input({ label, placeholder }) { return ( <label> {label} <input placeholder={placeholder} /> </label> ); } -> Option B

4. Quick Check:

   Destructure props and use inside JSX with curly braces [OK]

Hint: Destructure props and use inside JSX with curly braces [OK]

Common Mistakes:

• Using prop names as plain text instead of expressions
• Putting placeholder text in wrong prop
• Mixing label and placeholder positions