[gatsby-link] Make it usable outside Gatsby

[rstacruz]

Description

If you try to use <Link /> outside of Gatsby (eg, when running tests), it fails because the component tree doesn't have the context injected by Gatsby:

    TypeError: Cannot read property 'history' of undefined

      at new GatsbyLink (node_modules/gatsby-link/index.js:107:34)
      at constructClassInstance (node_modules/react-dom/cjs/react-dom.development.js:6355:20)
      at updateClassComponent (node_modules/react-dom/cjs/react-dom.development.js:7839:9)

It'd be nice if <Link /> will fallback to a common <a href=...> in the absence of this context.

Example

If you have a component (eg, MyMenu.js) that uses gatsby-link:

import * as React from 'react'
import Link from 'gatsby-link'

export const MyMenu = () => (
  <nav>
    <Link to='/'>Home</Link>
  </nav>
)

And have a test file that renders with it (using Jest syntax here, but it doesn't matter what test harness you use):

import * as React from 'react'
import { render } from 'react-dom'
import MyMenu from '../MyMenu'

it('works', () => {
  const div = document.createElement('div')
  render(<MyMenu />, div)
})

You'll get ⚠️ TypeError: Cannot read property 'history' of undefined.

Environment

• Gatsby version (npm list gatsby): gatsby@1.9.236
• gatsby-cli version (gatsby --version): n/a
• Node.js version: 8.10.0
• Operating System: Linux

[KyleAMathews]

Hmmm yeah. What do people normally do when testing components that rely on context?

[phs1919]

I had the same issue when testing Gatsby Link. This comment was useful to solve it. Hope this helps you :)

[rstacruz]

Testing things with context? It really depends. I typically do one of two things:

1. Create a context-less version (eg, <MediaPlayerView>) that's used by a "connector" component (eg, <MediaPlayer>) which will convert context stuff into props. I can now just test the <MediaPlayerView> component.

2. Create a mock context.

Anyway, I'd really love for this for react-storybook too, so I can make storybook pages out of my components that use gatsby-link!

[KyleAMathews]

Perhaps it'd be best to just create a context-less version? Can react-storybook do aliases? E.g. in there just create a component that wraps <a>. gatsby-link just has a bunch of logic necessary to make Gatsby page loading work, etc.

[varya]

I have the same problem. Is it possible to provide a property which would render Link but not access context things? This way it would be visible how it looks. This is what testing cares about.

[gatsbot]

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[gatsbot]

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