npm and error messages

node_modules/webpack-sources/lib/Source.js

@@ -0,0 +1,45 @@
+/*
+	MIT License http://www.opensource.org/licenses/mit-license.php
+	Author Tobias Koppers @sokra
+*/
+"use strict";
+
+var SourceNode = require("source-map").SourceNode;
+var SourceMapConsumer = require("source-map").SourceMapConsumer;
+
+class Source {
+
+	source() {
+		throw new Error("Abstract");
+	}
+
+	size() {
+		return this.source().length;
+	}
+
+	map(options) {
+		return null;
+	}
+
+	sourceAndMap(options) {
+		return {
+			source: this.source(),
+			map: this.map()
+		};
+	}
+
+	node() {
+		throw new Error("Abstract");
+	}
+
+	listNode() {
+		throw new Error("Abstract");
+	}
+
+	updateHash(hash) {
+		var source = this.source();
+		hash.update(source || "");
+	}
+}
+
+module.exports = Source;