freeCodeCamp/curriculum/challenges/chinese/03-front-end-libraries/react/use-default-props.md

---
id: 5a24c314108439a4d403616b
title: Use Default Props
challengeType: 6
forumTopicId: 301418
dashedName: use-default-props
---

# --description--

React also has an option to set default props. You can assign default props to a component as a property on the component itself and React assigns the default prop if necessary. This allows you to specify what a prop value should be if no value is explicitly provided. For example, if you declare `MyComponent.defaultProps = { location: 'San Francisco' }`, you have defined a location prop that's set to the string `San Francisco`, unless you specify otherwise. React assigns default props if props are undefined, but if you pass `null` as the value for a prop, it will remain `null`.

# --instructions--

The code editor shows a `ShoppingCart` component. Define default props on this component which specify a prop `items` with a value of `0`.

# --hints--

The `ShoppingCart` component should render.

```js
assert(
  (function () {
    const mockedComponent = Enzyme.mount(React.createElement(ShoppingCart));
    return mockedComponent.find('ShoppingCart').length === 1;
  })()
);
```

The `ShoppingCart` component should have a default prop of `{ items: 0 }`.

```js
assert(
  (function () {
    const mockedComponent = Enzyme.mount(React.createElement(ShoppingCart));
    mockedComponent.setProps({ items: undefined });
    return mockedComponent.find('ShoppingCart').props().items === 0;
  })()
);
```

# --seed--

## --after-user-code--

```jsx
ReactDOM.render(<ShoppingCart />, document.getElementById('root'))
```

## --seed-contents--

```jsx
const ShoppingCart = (props) => {
  return (
    <div>
      <h1>Shopping Cart Component</h1>
    </div>
  )
};
// Change code below this line
```

# --solutions--

```jsx
const ShoppingCart = (props) => {
  return (
    <div>
      <h1>Shopping Cart Component</h1>
    </div>
  )
};

// Change code below this line
ShoppingCart.defaultProps = {
  items: 0
}
```