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website/node_modules/npm/lib/install/is-only-optional.js

@@ -0,0 +1,19 @@
+'use strict'
+module.exports = isOptional
+
+const isOptDep = require('./is-opt-dep.js')
+
+function isOptional (node, seen) {
+  if (!seen) seen = new Set()
+  // If a node is not required by anything, then we've reached
+  // the top level package.
+  if (seen.has(node) || node.requiredBy.length === 0) {
+    return false
+  }
+  seen.add(node)
+  const swOptional = node.fromShrinkwrap && node.package._optional
+  return node.requiredBy.every(function (req) {
+    if (req.fakeChild && swOptional) return true
+    return isOptDep(req, node.package.name) || isOptional(req, seen)
+  })
+}