Return the empty string if negative

This closes #47

Author: yamadapc

lib/index.js

@@ -45,6 +45,10 @@ function writtenNumber(n, options) {
   options = options || {};
   options = util.defaults(options, writtenNumber.defaults);
 
+  if (n < 0) {
+    return "";
+  }
+
   n = Math.round(+n);
 
   var language = typeof options.lang === "string"

test/index.test.js

@@ -13,6 +13,11 @@ describe("written-number", function() {
       writtenNumber.should.be.instanceof(Function);
     });
 
+    it("negative numbers return \"\"", function() {
+      writtenNumber(-3).should.equal("");
+      writtenNumber(-5).should.equal("");
+    });
+
     it("doesn't blow up weirdly with invalid input", function() {
       writtenNumber("asdfasdfasdf").should.equal("");
       writtenNumber("0.as").should.equal("");