Spec compliant Int sizing

As discussed in #182, this was a deviation between spec and reference implementation, where the spec is more reasonable.

This tightens the allowed range of Int values to valid 32-bit signed integers, supporting the broadest collection of platforms.

For those who stumble upon this rev looking for ways to represent numeric-looking large values, see ID or Custom Scalars.

Author: leebyron

src/type/__tests__/serialization.js

@@ -41,14 +41,15 @@ describe('Type System: Scalar coercion', () => {
     expect(
       GraphQLInt.serialize(1e5)
     ).to.equal(100000);
-    // Bigger than 2^32, but still representable as an Int
+    // Maybe a safe JavaScript int, but bigger than 2^32, so not
+    // representable as a GraphQL Int
     expect(
       GraphQLInt.serialize(9876504321)
-    ).to.equal(9876504321);
+    ).to.equal(null);
     expect(
       GraphQLInt.serialize(-9876504321)
-    ).to.equal(-9876504321);
-    // Too big to represent as an Int
+    ).to.equal(null);
+    // Too big to represent as an Int in JavaScript or GraphQL
     expect(
       GraphQLInt.serialize(1e100)
     ).to.equal(null);

src/type/scalars.js

@@ -11,11 +11,13 @@
 import { GraphQLScalarType } from './definition';
 import { Kind } from '../language';
 
-// Integers are only safe when between -(2^53 - 1) and 2^53 - 1 due to being
-// encoded in JavaScript and represented in JSON as double-precision floating
-// point numbers, as specified by IEEE 754.
-var MAX_INT = 9007199254740991;
-var MIN_INT = -9007199254740991;
+// As per the GraphQL Spec, Integers are only treated as valid when a valid
+// 32-bit signed integer, providing the broadest support across platforms.
+//
+// n.b. JavaScript's integers are safe between -(2^53 - 1) and 2^53 - 1 because
+// they are internally represented as IEEE 754 doubles.
+var MAX_INT = 2147483647;
+var MIN_INT = -2147483648;
 
 function coerceInt(value) {
   var num = Number(value);