prune: check package.json before running

Fixes #3755.

1 files changed, 14 insertions, 2 deletions

diff --git a/lib/prune.js b/lib/prune.js
index 2afb2b998..0e13da13b 100644
--- a/lib/prune.js
+++ b/lib/prune.js
@@ -6,14 +6,26 @@ prune.usage = "npm prune"
 
 var readInstalled = require("read-installed")
   , npm = require("./npm.js")
+  , path = require("path")
+  , readJson = require("read-package-json")
+  , log = require("npmlog")
 
 prune.completion = require("./utils/completion/installed-deep.js")
 
 function prune (args, cb) {
-  readInstalled(npm.prefix, npm.config.get("depth"), function (er, data) {
+  //check if is a valid package.json file
+  var jsonFile = path.resolve(npm.dir, "..", "package.json" )
+  readJson(jsonFile, log.warn, function (er, data) {
     if (er) return cb(er)
-    prune_(args, data, cb)
+    next()
   })
+
+  function next() {
+    readInstalled(npm.prefix, npm.config.get("depth"), function (er, data) {
+      if (er) return cb(er)
+      prune_(args, data, cb)
+    })
+  }
 }
 
 function prune_ (args, data, cb) {