diff --git a/src/manifest/npm/mod.rs b/src/manifest/npm/mod.rs
index c8d65821..789cef06 100644
--- a/src/manifest/npm/mod.rs
+++ b/src/manifest/npm/mod.rs
@@ -7,6 +7,10 @@ pub use self::commonjs::CommonJSPackage;
 pub use self::esmodules::ESModulesPackage;
 pub use self::nomodules::NoModulesPackage;
 
+use error::Error;
+use std::fmt;
+use std::str::FromStr;
+
 #[derive(Serialize)]
 #[serde(untagged)]
 pub enum NpmPackage {
@@ -14,3 +18,33 @@ pub enum NpmPackage {
     ESModulesPackage(ESModulesPackage),
     NoModulesPackage(NoModulesPackage),
 }
+
+impl Default for NpmPackage {
+    fn default() -> NpmPackage {
+        ESModulesPackage {}
+    }
+}
+
+impl FromStr for NpmPackage {
+    type Err = Error;
+
+    fn from_str(s: &str) -> Result<Self, Error> {
+        match s {
+            "nodejs" => Ok(NpmPackage::CommonJSPackage),
+            "nomodules" => Ok(NpmPackage::NoModulesPackage),
+            _ => Err(Error::Unsupported {
+                message: format!("{} is not a supported target module type.", s),
+            }),
+        }
+    }
+}
+
+impl fmt::Display for NpmPackage {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        let printable = match *self {
+            CommonJSPackage => "--nodejs",
+            NoModulesPackage => "--no-modules",
+        };
+        write!(f, "{}", printable)
+    }
+}