1 files changed, 18 insertions, 0 deletions
diff --git a/deps/npm/lib/install/is-only-optional.js b/deps/npm/lib/install/is-only-optional.js
new file mode 100644
index 0000000000..7366e9abe1
--- /dev/null
+++ b/deps/npm/lib/install/is-only-optional.js
@@ -0,0 +1,18 @@
+'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)
+
+  return node.requiredBy.every(function (req) {
+    return isOptDep(req, node.package.name) || isOptional(req, seen)
+  })
+}