[v2] better error message when useField is used above Formik (TypeError: formik.getFieldProps is not a function)

🐛 Bug report

Current Behavior

using useField above a Formik instance generates this error:

Uncaught TypeError: formik.getFieldProps is not a function
    at useField (formik.esm.js:993)
    at NewReview (NewReview.tsx:41)

Expected behavior

a nicer error message

Reproducible example

import React from "react";
import { render } from "react-dom";
import { Formik, useField } from "formik";

import { DisplayFormikState } from "./helper";
import "./style.css";

const App = () => {
  const [field, meta] = useField("name"); // this is wrong usage
  return (
    <div className="app">
      <Formik
        initialValues={{ name: "" }}
        onSubmit={() => {}}
      >
        {props => {
          /**
           * Add your code here
           */
          return (
            <form onSubmit={props.handleSubmit}>
              <h1>Your code here</h1>
              <button type="submit">Submit</button>

              <DisplayFormikState {...props} />
            </form>
          );
        }}
      </Formik>
    </div>
  );
};

render(<App />, document.getElementById("root"));

https://codesandbox.io/s/formik-codesandbox-template-4yqz7

Suggested solution(s)

lets have a nicer error? if formik.getFieldProps doesnt exist, warn the user that they’re using formik wrong

Your environment

Software	Version(s)
Formik	2.x
React	16.8
TypeScript	3
Browser	chrome
npm/Yarn	6
Operating System	mac

[Granipouss]

Hello !

I dug a bit into this, it fails because it was used outside of a Formik context. There is a protection for it that should have triggered (see invariant in ./src/FormikContext.tsx). The thing is the default value of the context is set to {} on line 5. Meaning that if you don’t set a context, there will still be a non-null context, thus, the warning will not trigger.

An easy fix would be to replace the default value with undefined, I think. Thanks for signaling this bug.

[jzucadi]

Is there a solution to this?