Necessary Concepts to Build the Dictionary App

In this module, we will cover the essential React concepts that make our Dictionary App work. These include components, state with hooks, event handling, controlled inputs, side effects with useEffect, arrays and mapping, conditional rendering, and API integration with fetch. Understanding these will help you see how the app searches for words, fetches results, handles errors, and suggests alternative words.

1) Components

A React component is a reusable function that returns UI in JSX form. In our app, everything lives inside one main component called App.

• The App function handles state, API calls, and UI rendering.
• We didn’t break the app into smaller components, but if it grows, we could create separate ones for the search form, suggestions list, and results display.
• The App component defines both what the app looks like (input, results, suggestions) and how it behaves (fetching data, handling errors, updating state).

2) State and Hooks

State allows React apps to “remember” values and automatically update the UI when those values change. We used the useState hook for this.
Examples from our code:

const [word, setWord] = useState("");

const [results, setResults] = useState(null);

const [error, setError] = useState(null);

const [suggestions, setSuggestions] = useState([]);

• word stores the text typed by the user.
• results holds the fetched dictionary data (definitions, phonetic, synonyms).
• error stores error messages (like “Word not found”).
• suggestions keeps a list of alternative words.

When we call functions like setWord or setResults, React re-renders automatically, so the UI always matches the latest state.

3) Event Handling

Event handling lets the app respond to user actions.

Handling input typing:

<input

type="text"

placeholder="Enter a word..."

value={word}

onChange={(e) => setWord(e.target.value)}

/>

Whenever the user types, setWord updates the state with the new value.

Handling form submission:

<form onSubmit={handleSubmit}>

...

</form>

When the form is submitted, handleSubmit prevents the page reload, calls the API, and updates results or error state.

4) Controlled Inputs

In React, input fields are usually “controlled,” meaning their values are tied directly to state.
For example:

<input

type="text"

value={word}

onChange={(e) => setWord(e.target.value)}

/>

Here, the value comes from React state, and onChange updates that state as the user types. This ensures the input and state are always in sync, which is useful for validation, resetting, or passing the input to APIs.

5) Side Effects with useEffect

The useEffect hook lets us run code when the component renders or when a value changes. In our app, we used it to fetch word suggestions whenever the user types.
Example:

useEffect(() => {

if (word.length > 1) {

fetch(`https://api.datamuse.com/sug?s=${word}`)

.then((res) => res.json())

.then(async (data) => { ... })

.catch(() => setSuggestions([]));

} else {

setSuggestions([]);

}

}, [word]);

• The dependency [word] means this effect runs every time word changes.
• If the user types at least two letters, suggestions are fetched from the Datamuse API.
• This keeps the UI interactive and responsive to user input.

6) Arrays and Mapping

Arrays help us render multiple items dynamically using map().

Rendering suggestions:

{suggestions.slice(0, 5).map((sug, i) => (

<button key={i} onClick={() => setWord(sug)}>

{sug}

</button>

))}

Here, each suggestion is turned into a button. Clicking the button sets that suggestion as the new word.

Rendering definitions:

{results.definitions.map((def, index) => (

<li key={index}>

<strong>{def.partOfSpeech}:</strong> {def.definition}

</li>

))}

This creates a list item for each definition dynamically, depending on what the API returns.

7) Conditional Rendering

We only want to display certain parts of the UI when data is available. React makes this simple with conditional rendering.

Showing suggestions only if they exist:

{suggestions.length > 0 && (

<div className="suggestions">...</div>

)}

Showing results only when results is set:

{results && (

<div className="results">...</div>

)}

This way, we avoid showing empty or irrelevant sections.

8) API Integration with Fetch

Our app relies on two APIs:

1. Dictionary API: Fetches definitions and details for a word.
2. Datamuse API: Suggests possible words based on user input.

Example of fetching dictionary data:

const res = await fetch(

`https://api.dictionaryapi.dev/api/v2/entries/en/${word}`

);

• If the response is valid, we parse it with res.json() and extract word details.
• If not, we set an error message in state.

By combining fetch with state, we ensure that the app updates instantly with either results, suggestions, or an error.

By understanding these concepts—components, state, event handling, controlled inputs, useEffect, arrays, conditional rendering, and API integration—you now have the foundation for how this dictionary app works. These ideas are the building blocks of many real-world React applications.