Show all episodes in Netlify deploy previews

[Steellow]

Fixes #79.

[netlify]

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[mtsknn]

Rhetorical question: what does this do?

I think it's not obvious at a glance, so I created a truth table (1 = true, 0 = false):

is prod build	is scheduled	is deploy preview		is prod build && is scheduled	!(is prod build && is scheduled)	!(is prod build && is scheduled) || is deploy preview
1	1	1		1	0	1
1	1	0		1	0	0
1	0	1		0	1	1
0	1	1		0	1	1
1	0	0		0	1	1
0	1	0		0	1	1
0	0	1		0	1	1
0	0	0		0	1	1

And here's a simpler truth table with descriptions in English (notice how the rightmost column is identical to the previous table's rightmost column except here I'm using the words "yes" and "no" instead of 1 and 0):

is prod build	is scheduled	is deploy preview	should this episode be included?
1	1	1	yes because is deploy preview
1	1	0	no
1	0	1	yes because is not scheduled / is deploy preview
0	1	1	yes because is dev build / deploy preview (invalid combo because deploy previews are always prod builds)
1	0	0	yes because is not scheduled
0	1	0	yes because is dev build
0	0	1	yes because is dev build / not scheduled / is deploy preview (invalid combo; see above)
0	0	0	yes because is dev build / not scheduled

All right, so .filter() should return false only when isProdBuild() && isScheduled() && !isNetlifyDeployPreview(). Like so:

.filter(
  (episode) => !(isProdBuild() && isScheduled(episode) && !isNetlifyDeployPreview())
)

Would that be easier to grasp? Or maybe move isScheduled() to the beginning so it's clearer that this filtering is about scheduled episodes:

.filter(
  (episode) => !(isScheduled(episode) && isProdBuild() && !isNetlifyDeployPreview())
)

Using one of De Morgan's laws – !(A && B) === !A || !B – the conditional could be flipped on its head:

.filter(
  (episode) => !isScheduled(episode) || !isProdBuild() || isNetlifyDeployPreview()
)

The conditional could be even easier to read if we created a new util isDevBuild():

.filter(
  (episode) => !isScheduled(episode) || isDevBuild() || isNetlifyDeployPreview()
)

Hmm, I take my words back – I think the conditional is clearer if isScheduled() is at the end:

.filter(
  (episode) => isDevBuild() || isNetlifyDeployPreview() || !isScheduled(episode)
)

Now it reads like English: "include all episodes in dev builds and Netlify deploy previews; otherwise include non-scheduled episodes." I think this would be the best option!

Which one is the best in your opinion?

[mtsknn]

• We already have a util called isNetlifyProdEnv(), so isNetlifyDeployPreview() would have a more consistent name.
• The check should be against process.env.CONTEXT, not process.env.NODE_ENV.
• With a similar JSDoc comment as in isNetlifyProdEnv(), the code could look like this:

Suggested change

	/**
	* Checks whether the current build is a deploy preview build.
	*
	* @returns {boolean}
	*/
	export const isPreviewBuild = () => process.env.NODE_ENV === 'deploy-preview'
	/**
	* Checks whether the current build is a Netlify deploy preview.
	* Netlify does automatic deploy previews for pull requests.
	*
	* Returns `false` in non-Netlify environments, e.g. localhost.
	*
	* @see {@link https://docs.netlify.com/configure-builds/environment-variables/#build-metadata}
	*
	* @returns {boolean}
	*/
	export const isNetlifyDeployPreview = () => process.env.CONTEXT === 'deploy-preview'

I would also:

• Move this util to the beginning of the file so that all utils are sorted alphabetically.
• Simplify the JSDoc comment of isNetlifyProdEnv():

/**
 * Checks whether the current build is against Netlify's production.
 *
 * Returns `false` in non-Netlify environments, e.g. localhost.
 *
 * @see {@link https://docs.netlify.com/configure-builds/environment-variables/#build-metadata}
 *
 * @returns {boolean}
 */
export const isNetlifyProdEnv = () => process.env.CONTEXT === 'production'

[mtsknn]

Can't be merged yet because at least this change is necessary:

-process.env.NODE_ENV === 'deploy-preview'
+process.env.CONTEXT === 'deploy-preview'