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fix(gatsby-link): Do not crash in unit tests when globals are undefined #25608

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Jul 10, 2020
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4 changes: 2 additions & 2 deletions packages/gatsby-link/src/__tests__/index.js
Original file line number Diff line number Diff line change
Expand Up @@ -94,8 +94,8 @@ describe(`<Link />`, () => {
})

it(`does not fail with missing __BASE_PATH__`, () => {
global.__PATH_PREFIX__ = ``
global.__BASE_PATH__ = undefined
delete global.__PATH_PREFIX__
delete global.__BASE_PATH__

const source = createMemorySource(`/active`)

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21 changes: 18 additions & 3 deletions packages/gatsby-link/src/index.js
Original file line number Diff line number Diff line change
Expand Up @@ -9,29 +9,44 @@ export { parsePath }

const isAbsolutePath = path => path?.startsWith(`/`)

export function withPrefix(path, prefix = __BASE_PATH__) {
export function withPrefix(path, prefix = getGlobalBasePrefix()) {
if (!isLocalLink(path)) {
return path
}

if (path.startsWith(`./`) || path.startsWith(`../`)) {
return path
}
const base = prefix ?? __PATH_PREFIX__ ?? `/`
const base = prefix ?? getGlobalPathPrefix() ?? `/`

return `${base?.endsWith(`/`) ? base.slice(0, -1) : base}${
path.startsWith(`/`) ? path : `/${path}`
}`
}

// These global values are wrapped in typeof clauses to ensure the values exist.
// This is especially problematic in unit testing of this component.
const getGlobalPathPrefix = () =>
process.env.NODE_ENV !== `production`
? typeof __PATH_PREFIX__ !== `undefined`
? __PATH_PREFIX__
: undefined
: __PATH_PREFIX__
Comment on lines +29 to +34
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@ascorbic ascorbic Jul 9, 2020

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Nested ternaries are really hard to read. How about

Edit: oops

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Ironically, the ternary confused me so I misunderstood what was happening! I see what you're doing, but I'd still rather replafe the ternary with an early return.

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In the context of this discussion; I prefer to use === over !== if there is an else branch unless there's a clear reason to show the !== branch first. I think it reads better as inverting adds to the mental overhead of parsing code. I agree with Matt that this one is a little hairy. Sometimes it is what it is.

I would consider to ignore the production check (what purpose does that serve?) since it currently assumes the var exists in production anyways, so typeof __PATH_PREFIX__ === 'undefined' should be false regardless. So I'd suggest this instead.

Suggested change
const getGlobalPathPrefix = () =>
process.env.NODE_ENV !== `production`
? typeof __PATH_PREFIX__ !== `undefined`
? __PATH_PREFIX__
: undefined
: __PATH_PREFIX__
const getGlobalPathPrefix = () =>
// Prevent reference error; the `__PATH_PREFIX__` binding may not exist in tests
typeof __PATH_PREFIX__ === `undefined` ? undefined : __PATH_PREFIX__

const getGlobalBasePrefix = () =>
process.env.NODE_ENV !== `production`
? typeof __BASE_PATH__ !== `undefined`
? __BASE_PATH__
: undefined
: __BASE_PATH__

const isLocalLink = path =>
path &&
!path.startsWith(`http://`) &&
!path.startsWith(`https://`) &&
!path.startsWith(`//`)

export function withAssetPrefix(path) {
return withPrefix(path, __PATH_PREFIX__)
return withPrefix(path, getGlobalPathPrefix())
}

function absolutify(path, current) {
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