Fix for formatDecimal when p is undefined.

src/formatDecimal.js

@@ -2,7 +2,7 @@
 // significant digits p, where x is positive and p is in [1, 21] or undefined.
 // For example, formatDecimal(1.23) returns ["123", -1].
 export default function(x, p) {
-  if ((i = (x = x.toExponential(p - 1)).indexOf("e")) < 0) return null; // NaN, ±Infinity
+  if ((i = (x = x.toExponential(p && p - 1)).indexOf("e")) < 0) return null; // NaN, ±Infinity
   var i, coefficient = x.slice(0, i);
 
   // The string returned by toExponential either has the form \d\.\d+e[-+]\d+

test/precisionFixed-test.js

@@ -0,0 +1,12 @@
+var tape = require("tape"),
+    format = require("../");
+
+tape("precisionFixed(number) returns the expected value", function(test) {
+  test.equal(format.precisionFixed(8.9), 0);
+  test.equal(format.precisionFixed(1.1), 0);
+  test.equal(format.precisionFixed(0.89), 1);
+  test.equal(format.precisionFixed(0.11), 1);
+  test.equal(format.precisionFixed(0.089), 2);
+  test.equal(format.precisionFixed(0.011), 2);
+  test.end();
+});