I think this fixes IE11 compatibility

package.json

@@ -74,6 +74,7 @@
     "react": "^0.14.0"
   },
   "dependencies": {
-    "invariant": "^2.1.2"
+    "invariant": "^2.1.2",
+    "lodash.isfinite": "^3.3.1"
   }
 }

src/abstract-number-format-input/index.js

@@ -4,6 +4,7 @@ import escapeRegExp from './util/escapeRegExp';
 import indexOfLastDigit from './util/indexOfLastDigit';
 import invariant from 'invariant';
 import nextPosition from './nextPosition';
+import isFinite from 'lodash.isfinite';
 
 function indexOfDigit(str, start, direction) {
   let pos = start;
@@ -51,7 +52,7 @@ export default function createAbstractNumberFormatInput(numberFormat) {
   function format(number) {
     if (number === null || number === undefined) return '';
     if (typeof number === 'string') return format(parse(number));
-    invariant(Number.isFinite(number), `Illegal number value: ${JSON.stringify(number)}`);
+    invariant(isFinite(number), `Illegal number value: ${JSON.stringify(number)}`);
     return addTrailingZeros(numberFormat.format(number));
   }
 

src/abstract-number-format-input/util/parseNumber.js

@@ -1,5 +1,6 @@
 import escapeRegExp from './escapeRegExp';
 import invariant from 'invariant';
+import isFinite from 'lodash.isfinite';
 
 function assertZeroOrOneDecimalChar(str, decimalChar) {
   if (!decimalChar) return;
@@ -20,7 +21,7 @@ export default function parseNumber(formattedNumber, decimalChar) {
   invariant(numberStr.lastIndexOf('-') <= 0, `Misplaced minus sign in '${numberStr}'`);
 
   const number = parseFloat(numberStr);
-  invariant(Number.isFinite(number), `parseFloat was unable to parse '${numberStr}'`);
+  invariant(isFinite(number), `parseFloat was unable to parse '${numberStr}'`);
 
   return number;
 }