# React Vs Qwik

Several examples comparing React and Qwik.

## Hello world component

### From React

```tsx
export const HelloWorld = () => {
  return <div>Hello world</div>;
}
```

### To Qwik

```tsx
export const HelloWorld = component$(() => {
  return <div>Hello world</div>;
});
```

**What is component$ and $?**

component$ is used to declare a [Qwik component.](https://qwik.dev/docs/core/overview/#component)

[The dollar sign](https://qwik.dev/docs/advanced/dollar/#the-dollar--sign) $ is used to signal both the optimizer and the developer when Qwik splits up your application into many small pieces we call symbols.

## Button with a click handler

### From React

```tsx
export const Button = () => {
  return <button onClick={() => console.log('click')}>Click me</button>;
}
```

### To Qwik

```tsx
export const Button = component$(() => {
  return <button onClick$={() => console.log('click')}>Click me</button>;
});
```

**Remember $?**

Event handlers in qwik behave in the same way as in other frameworks, you just have to keep in mind that their content will be loaded in a lazy way thanks to the dollar suffix.

Attention : JSX [handlers](https://qwik.dev/docs/core/events/#inline-handler) such as onClick$ and onInput$ are only executed on the client. This is because they are DOM events, since there is no DOM on the server, they will not be executed on the server.

## Declare local state

### From React

```tsx
export function UseStateExample() {
  const [value, setValue] = useState(0);
  return <div>Value is: {value}</div>;
}
```

### To Qwik

```tsx
export const LocalStateExample = component$(() => {
  const count = useSignal(0);
  return <div>Value is: {count.value}</div>;
});
```

**What if I have a more complex state?**

[useStore()](https://qwik.dev/docs/core/state/#usestore) Works very similarly to useSignal(), but it takes an object as its initial value and the reactivity extends to nested objects and arrays by default. One can think of a store as a multiple-value signal or an object made of several signals.

## Create a counter component

### From React

```tsx
export function Counter() {
  const [count, setCount] = useState(0);
  return (
    <>
      <p>Value is: {count}</p>
      <button onClick={() => setCount(count + 1)}>Increment</button>
    </>
  );
}
```

### To Qwik

```tsx
export const Counter = component$(() => {
  const count = useSignal(0);
  return (
    <>
      <p>Value is: {count.value}</p>
      <button onClick$={() => count.value++}>Increment</button>
    </>
  );
});
```

## Using Props

### From React

```tsx
export const Parent = (() => {
  const [ count, setCount ] = useState<number>(0);

  const increment = (() => {
    setCount((prev) => prev + 1)
  })
  return <Child count={count} increment={increment} />;
})

interface ChildProps {
  count: number;
  increment: () => void;
}

export const Child = ((props: ChildProps) => {
  return (
    <>
      <button onClick={props.increment}>Increment</button>
      <p>Count: {props.count}</p>
    </>
  );
})
```

### To Qwik

```tsx
export const Parent = component$(() => {
  const userData = useStore({ count: 0 });
  return <Child userData={userData} />;
});

interface ChildProps {
  userData: { count: number };
}

export const Child = component$<ChildProps>(({ userData }) => {
  return (
    <>
      <button onClick$={() => userData.count++}>Increment</button>
      <p>Count: {userData.count}</p>
    </>
  );
});
```

**Wait, I don't need to pass the handler as a prop?**

The reactive signal returned by [useSignal()](https://qwik.dev/docs/core/state/#usesignal) consists of an object with a single property .value. If you change the value property of the signal, any component that depends on it will be updated automatically.

## Create a clock that increments every second

### From React

```tsx
export function Clock() {
  const [seconds, setSeconds] = useState(0);
  useEffect(() => {
    const interval = setInterval(() => {
      setSeconds(seconds + 1);
    }, 1000);
    return () => clearInterval(interval);
  });
  return <p>Seconds: {seconds}</p>;
}
```

### To Qwik

```tsx
export const Clock = component$(() => {
  const seconds = useSignal(0);
  useVisibleTask$(({ cleanup }) => {
    const interval = setInterval(() => {
      seconds.value++;
    }, 1000);
    cleanup(() => clearInterval(interval));
  });

  return <p>Seconds: {seconds.value}</p>;
});
```

## Perform a fetch request every time the state changes

### From React

```tsx
export function Fetch() {
  const [url, setUrl] = useState('https://api.github.com/repos/QwikDev/qwik');
  const [responseJson, setResponseJson] = useState(undefined);

  useEffect(() => {
    fetch(url)
      .then((res) => res.json())
      .then((json) => setResponseJson(json));
  }, [url]);

  return (
    <>
      <p>{responseJson?.name} has {responseJson?.stargazers_count} 's</p>
      <input name="url" value={url} onChange={(e) => setUrl(e.target.value)} />
    </>
  );
}
```

### To Qwik

```tsx
export const Fetch = component$(() => {
  const url = useSignal('https://api.github.com/repos/QwikDev/qwik');
  const responseJson = useSignal(undefined);

  useTask$(async ({ track }) => {
    track(() => url.value);
    const res = await fetch(url.value);
    const json = await res.json();
    responseJson.value = json;
  });

  return (
    <>
      <p>{responseJson.value?.name} has {responseJson.value?.stargazers_count} 's</p>
      <input name="url" bind:value={url} />
    </>
  );
});
```

**What is useTask$ and bind?**

[useTask$()](https://qwik.dev/docs/core/tasks/#usetask) registers a hook to be executed upon component creation, it will run at least once either in the server or in the browser, depending on where the component is initially rendered.

[bind attribute](https://qwik.dev/docs/core/rendering/#bind-attribute) is a convenient API to two-way data bind the value of an `input` to a Signal.

## Declare some context and consume it

### From React

```tsx
export const MyContext = createContext({ message: 'some example value' });

export default function Parent() {
  return (
    <MyContext.Provider value={{ message: 'updated example value' }}>
      <Child />
    </MyContext.Provider>
  );
}

export const Child = () => {
  const value = useContext(MyContext);
  return <p>{value.message}</p>;
};
```

### To Qwik

```tsx
export const MyContext = createContextId('my-context');

export const Parent = component$(() => {
  const message = useSignal('some example value');
  useContextProvider(MyContext, message);
  return (
    <>
      <Child />
    </>
  );
});

export const Child = component$(() => {
  const message = useContext(MyContext);
  return <p>{message.value}</p>;
});
```

**How can I avoid prop drilling?**

You simply need to create a [context](https://qwik.dev/docs/core/context/#context).

Just create the context in the component where you need to store the information and then, in its descendants, get the information through the corresponding ContextId.

## Create a debounced input

### From React

```tsx
export const DebouncedInput = () => {
  const [value, setValue] = useState('');
  const [debouncedValue, setDebouncedValue] = useState(value);

  useEffect(() => {
    const debounced = setTimeout(() => setDebouncedValue(value), 1000);
    return () => clearTimeout(debounced);
  }, [value]);

  return (
    <>
      <input
        value={value}
        onChange={(ev) => setValue((ev.target as HTMLInputElement).value)}
      />
      <p>{debouncedValue}</p>
    </>
  );
};
```

### To Qwik

```tsx
export const DebouncedInput = component$(() => {
  const inputText = useSignal('');
  const debouncedValue = useSignal('');

  useTask$(({ track, cleanup }) => {
    track(() => inputText.value);

    const debounced = setTimeout(() => {
      debouncedValue.value = inputText.value;
    }, 1000);
    cleanup(() => clearTimeout(debounced));
  });

  return (
    <>
      <input bind:value={inputText} />
      <p>{debouncedValue.value}</p>
    </>
  );
});
```

## Change background color randomly every button click

### From React

```tsx
export function DynamicBackground() {
  const [red, setRed] = useState(0);
  const [green, setGreen] = useState(0);
  const [blue, setBlue] = useState(0);
  return (
    <div
      style={{
        background: `rgb(${red}, ${green}, ${blue})`,
      }}
    >
      <button
        onClick={() => {
          setRed(Math.random() * 256);
          setGreen(Math.random() * 256);
          setBlue(Math.random() * 256);
        }}
      >
        Change background
      </button>
    </div>
  );
}
```

### To Qwik

```tsx
export const DynamicBackground = component$(() => {
  const red = useSignal(0);
  const green = useSignal(0);
  const blue = useSignal(0);

  return (
    <div
      style={{
        background: `rgb(${red.value}, ${green.value}, ${blue.value})`,
      }}
    >
      <button
        onClick$={() => {
          red.value = Math.random() * 256;
          green.value = Math.random() * 256;
          blue.value = Math.random() * 256;
        }}
      >
        Change background
      </button>
    </div>
  );
});
```

## Create a component that renders a list of the presidents

### From React

```tsx
export function Presidents() {
  const presidents = [
    { name: 'George Washington', years: '1789-1797' },
    { name: 'John Adams', years: '1797-1801' },
    { name: 'Thomas Jefferson', years: '1801-1809' },
    { name: 'James Madison', years: '1809-1817' },
    { name: 'James Monroe', years: '1817-1825' },
    { name: 'John Quincy Adams', years: '1825-1829' },
    { name: 'Andrew Jackson', years: '1829-1837' },
    { name: 'Martin Van Buren', years: '1837-1841' },
    { name: 'William Henry Harrison', years: '1841-1841' },
    { name: 'John Tyler', years: '1841-1845' },
    { name: 'James K. Polk', years: '1845-1849' },
    { name: 'Zachary Taylor', years: '1849-1850' },
    { name: 'Millard Fillmore', years: '1850-1853' },
    { name: 'Franklin Pierce', years: '1853-1857' },
    { name: 'James Buchanan', years: '1857-1861' },
    { name: 'Abraham Lincoln', years: '1861-1865' },
    { name: 'Andrew Johnson', years: '1865-1869' },
    { name: 'Ulysses S. Grant', years: '1869-1877' },
    { name: 'Rutherford B. Hayes', years: '1877-1881' },
    { name: 'James A. Garfield', years: '1881-1881' },
    { name: 'Chester A. Arthur', years: '1881-1885' },
    { name: 'Grover Cleveland', years: '1885-1889' },
  ];
  return (
    <ul>
      {presidents.map((president) => (
        <li key={president.name + president.years}>
          {president.name} ({president.years})
        </li>
      ))}
    </ul>
  );
}
```

### To Qwik

```tsx
export const Presidents = component$(() => {
  const presidents = [
    { name: 'George Washington', years: '1789-1797' },
    { name: 'John Adams', years: '1797-1801' },
    { name: 'Thomas Jefferson', years: '1801-1809' },
    { name: 'James Madison', years: '1809-1817' },
    { name: 'James Monroe', years: '1817-1825' },
    { name: 'John Quincy Adams', years: '1825-1829' },
    { name: 'Andrew Jackson', years: '1829-1837' },
    { name: 'Martin Van Buren', years: '1837-1841' },
    { name: 'William Henry Harrison', years: '1841-1841' },
    { name: 'John Tyler', years: '1841-1845' },
    { name: 'James K. Polk', years: '1845-1849' },
    { name: 'Zachary Taylor', years: '1849-1850' },
    { name: 'Millard Fillmore', years: '1850-1853' },
    { name: 'Franklin Pierce', years: '1853-1857' },
    { name: 'James Buchanan', years: '1857-1861' },
    { name: 'Abraham Lincoln', years: '1861-1865' },
    { name: 'Andrew Johnson', years: '1865-1869' },
    { name: 'Ulysses S. Grant', years: '1869-1877' },
    { name: 'Rutherford B. Hayes', years: '1877-1881' },
    { name: 'James A. Garfield', years: '1881-1881' },
    { name: 'Chester A. Arthur', years: '1881-1885' },
    { name: 'Grover Cleveland', years: '1885-1889' },
  ];
  return (
    <ul>
      {presidents.map((president) => (
        <li key={president.name + president.years}>
          {president.name} ({president.years})
        </li>
      ))}
    </ul>
  );
});
```