add getEnvVar function

Author: gregrickaby

lib/functions.js

@@ -2,18 +2,34 @@
 export const fetcher = (...args) => fetch(...args).then((res) => res.json()) // eslint-disable-line no-undef
 
 /**
- * On scroll, add or remove a "shrink" class.
+ * Retrieve environment-specific var.
  *
- * @param {object} el The header element.
+ * @param  {string} varName  Environment variable.
+ * @param  {bool}   isPublic Whether var is public.
+ * @return {string}          Env var value.
  */
-export function shrinkHeader(el) {
-  /* eslint-disable */
-  window.addEventListener('scroll', () => {
-    if (window.scrollY > 30) {
-      el.current.classList.add('shrink')
-    } else {
-      el.current.classList.remove('shrink')
-    }
-  })
-  /* eslint-enable */
+export function getEnvVar(varName, isPublic = false) {
+  const prefix = isPublic ? 'NEXT_PUBLIC_' : ''
+
+  // If var missing or currently in Vercel "dev" (local), use local settings.
+  if (!process.env.VERCEL_ENV || 'development' === process.env.VERCEL_ENV) {
+    return process.env[`${prefix}LOCAL_${varName}`]
+  }
+
+  // Prod / main / default.
+  if (
+    'production' === process.env.VERCEL_ENV ||
+    'preview' !== process.env.VERCEL_ENV
+  ) {
+    return process.env[`${prefix}PROD_${varName}`]
+  }
+
+  // Switch between staging and develop in Vercel "preview" env.
+  switch (process.env.VERCEL_GITHUB_COMMIT_REF) {
+    case 'staging':
+      return process.env[`${prefix}STAGING_${varName}`]
+    case 'develop':
+    default:
+      return process.env[`${prefix}DEV_${varName}`]
+  }
 }