Are you tired of dealing with tricky type issues when using React Context? Don't worry, we've got you covered! In this blog, we'll walk you through a step-by-step guide on how to tackle one of the most common challenges – working with Dark and Light themes using React Context and TypeScript. 🎉

Embracing Dark and Light Themes in JavaScript 🔮

Let's start by diving into the JavaScript implementation of our theme switching functionality. We'll create a custom hook and a component to toggle between dark and light themes. 🌗

Implementing the Magic ✨

let's try implementing it in javascript first :

• create theme getter and setter

• create a custom hook for ease of use across the application

import { createContext, useContext, useState } from "react";

export const ThemeContext = createContext();

const ThemeProvider = ({ children }) => {
  const [theme, setTheme] = useState("dark");
  return (
    <ThemeContext.Provider value={{ theme, setTheme }}>
      {children}
    </ThemeContext.Provider>
  );
};

export const useThemeContext=()=>{
const context = useContext(ThemeContext);
 //this ensures it is only called from components wrapped in themeContext Provider
    if(!context){
        throw new Error("themecontext should be used inside theme context provider");
     }
   return context
}

// src/components/ThemeSwitch.js

import { useThemeContext } from "./theme";

const ToggleTheme = () => {
  const { theme, setTheme } = useThemeContext();
  const otherTheme = theme === "dark" ? "light" : "dark";

  return (
    <div>
      <Button onClick={() => setTheme(otherTheme)}>
        Switch To {otherTheme} Mode
      </Button>
    </div>
  );
};

Adding Some TypeScript Spice 🌶️

While the JavaScript implementation gets the job done, TypeScript can save us from unexpected errors and provide better code understanding. Let's address the pain points one by one.

1. Default Value Dilemma 🤔

Problem:

export const ThemeContext = createContext();

Solution:

1. When the context is initially defined:

export const ThemeContext = createContext({
  theme: 'dark',
  setTheme: (theme: string) => {},
});

1. When the context is initially undefined:

type ContextType = {
  theme: string,
  setTheme: (theme: string) => void
};

export const ThemeContext = createContext<ContextType | undefined>(undefined);

2. Type-Checked Props with PropsWithChildren 🎈

what is PropsWithChildren?

PropsWithChildren type takes your component prop and returns a union type with the children prop appropriately typed.

Solution:

1. When the context is initially defined:

export const ThemeProvider = ({ children }: PropsWithChildren<{}>) => {...}

1. When the context is initially undefined:

   
    type ContextType={
        theme:string,
        setTheme:(theme:string)=> void
    }
   
    //wrong:
    export const ThemeProvider = ({ children }: PropsWithChildren<{}>) => {
      const [theme, setTheme] = useState("");
     /*ISSUE: in usestate theme ; Type 'undefined' is not assignable to type 'string'. */
   
    //possible solution:
    export const ThemeProvider = ({ children }: PropsWithChildren<{}>) => {
      const [theme, setTheme] = useState<ContextType["theme"]>();
   
      /*ISSUE: Type 'string | undefined' is not assignable to type 'string'. Type 'undefined' is not assignable to type 'string'.*/
   

Currently, the state is ContextType['theme'] | undefined, but the context type expects a ContextType['theme'] for that property. To fix this, the simplest solution is to explicitly pass a default value of the same type as the context value. In our case, this would be an empty string.

const [theme, setTheme] = useState<ContextType['theme']>('');

This ensures that the theme type is consistently a string, never undefined. Your context is now beautifully typed!

A Flawless Finale 🌟

After overcoming these TypeScript hurdles, your code will not only be more robust but also cleaner and easier to understand. Here's the final code snippet:

import { PropsWithChildren, createContext, useContext, useState } from "react";

type ContextType = { theme: string; setTheme: (theme: string) => void };

export const ThemeContext = createContext<ContextType | undefined>(undefined);

export const ThemeProvider = ({ children }: PropsWithChildren<{}>) => {
  const [theme, setTheme] = useState<ContextType["theme"]>("");

  return (
    <ThemeContext.Provider value={{ theme, setTheme }}>
      {children}
    </ThemeContext.Provider>
  );
};

export const useThemeContext = () => {
  const context = useContext(ThemeContext);

  if (!context) {
    throw new Error("useThemeContext must be used inside the ThemeProvider");
  }

  return context;
};