Context API is a feature in ReactJS that is often used as a replacement for Redux or other state management libraries because it allows for simpler data flow in an application.

Here is how it can be used:

1. Create Context: First step is to create a context.

```
const MyContext = React.createContext(defaultValue);
```
The defaultValue argument is only used when a component does not have a matching Provider.

1. Create Context Provider: To pass the data through the component tree, create a context provider. All the components that are children of this provider will have access to the context.

```

```

The provider accepts a `value` prop to be passed to consuming components that are descendants of this Provider.

1. Consume Context: After provider is set, we can access the value in any child component by using the `React.useContext()` hook.

```
const contextValue = React.useContext(MyContext);
```
Or you can use the `Context.Consumer` component.

```
{value => /* render something based on the context value */}

```

Context API is primarily used when some data needs to be accessible by many components at different nesting levels.

Here is a complete example using the Context API in React:

```
import React, { createContext, useState } from ‘react’;

// Step1: create your context
const NumberContext = createContext();

const App = () => { // we pass this value down the component tree using provider const [number, setNumber] = useState(0);

return (

); }

const Display = () => { const { number } = useContext(NumberContext);

return

{number}

}

const Increment = () => { const { number, setNumber } = useContext(NumberContext);

return }

export default App;
```
We created a basic counter with a display and increment button where state is shared between the two components using Context API. Notice how easy it is to share state and change it from different components.

How to use the Context API in Reactjs?

{number}