React.useContext appearing as undefined

This is my first time using the React context hooks in an app and my context default value keeps appearing as "undefined."

Troubleshooting so far:

• I've made sure React.createContext is in a separate file (context.js)
• I've made sure the child component is wrapped within the Provider
• I'm providing a default value to React.createContext()

All of my code can be found in this CodeSandbox link below:

https://codesandbox.io/s/react-context-troubleshooting-ojnb2?file=/src/child.js

In your App.js file, you're passing value a string:

import React, { useContext } from "react";
import { SelectedBackgroundContext } from "./context";
import Child from "./child";

function App() {
  const { selectedBackground } = useContext(SelectedBackgroundContext);

  // selectedBackground is just a string, so value = "https://...", which is invalid, the value, in your case, should be an object
  return (
    <SelectedBackgroundContext.Provider value={selectedBackground}>
      <Child />
    </SelectedBackgroundContext.Provider>
  );
}

export default App;

Instead, value needs to be an object, with a selectedBackground property that contains the string:

import React, { useContext } from "react";
import { SelectedBackgroundContext } from "./context";
import Child from "./child";

function App() {
  const { selectedBackground, selectBackground } = useContext(
    SelectedBackgroundContext
  );
  // alternatively, just collect all context, without destructuring,
  // and pass it to the "value" prop: value={context}
  // const context = useContext(SelectedBackgroundContext);


  // you're also missing the "selectBackground" function, which should be added to this "value" prop
  return (
    <SelectedBackgroundContext.Provider
      value={{ selectedBackground, selectBackground }}
    >
      <Child />
    </SelectedBackgroundContext.Provider>
  );
}

export default App;

Since you've created context using an object:

{
  selectedBackground:
    "https://lp-cms-production.imgix.net/2019-06/81377873%20.jpg?fit=crop&q=40&sharp=10&vib=20&auto=format&ixlib=react-8.6.4",
  selectBackground: () => {}
}

The value property of the provider should also be an object!

value={{ selectedBackground, selectBackground }}

Working demo: