React Native Styled-Components Responsive Font - TypeScript

In this article, we'll explore how to use styled-components to make our font sizes both responsive and type-safe using TypeScript in a React Native app.

What are styled-components?

Styled-components is a popular library for styling React components. It allows us to write CSS in our JavaScript code, using tagged template literals. Styled-components provides a powerful and flexible way to style our components, with the added bonus of giving us type-safety if we're using TypeScript.

Font sizing in React Native

In React Native, we can set font sizes in a few different ways:

• Using pixel values: fontSize: 16
• Using scalable font size: fontSize: 16 * PixelRatio.getFontScale()
• Using relative font size: fontSize: 16 * Dimensions.get('window').width / 375

Setting font sizes using pixel values is simple, but it isn't responsive to different screen sizes. On the other hand, scalable font size and relative font size take into account the device's pixel density and screen width, respectively, making them more responsive. However, using these values directly can be error-prone and awkward.

Making font sizes responsive with styled-components

With styled-components, we can make our font sizes responsive and type-safe using the power of CSS and TypeScript.

First, let's define a theme object that contains font size values for various screen sizes:

interface Theme {
  fontSizes: {
    xs: number;
    sm: number;
    md: number;
    lg: number;
    xl: number;
  };
}

const theme: Theme = {
  fontSizes: {
    xs: 12,
    sm: 14,
    md: 16,
    lg: 18,
    xl: 20
  }
};

Next, let's define a Text component that accepts a fontSize prop, which maps to the font size values in our theme object. We can use the css helper from styled-components to define our styles:

import styled from 'styled-components/native';

interface TextProps {
  fontSize: keyof Theme['fontSizes'];
}

const Text = styled.Text<TextProps>`
  font-size: ${({ fontSize, theme }) => theme.fontSizes[fontSize]}px;
`;

Notice that we use keyof to map the fontSize prop to the keys of our Theme['fontSizes'] type. This ensures that we only accept valid font size values from our theme object.

Now we can use our Text component like this:

<Text fontSize="md">Hello World</Text>

The fontSize prop is now both type-safe and responsive to different screen sizes.

Conclusion

Styled-components is a powerful library for styling React components in a type-safe and responsive way. By defining a theme object and using the css helper, we can easily make font sizes responsive while keeping our code type-safe using TypeScript.