Add is.safeInteger() (#22)

index.js

@@ -124,6 +124,7 @@ const primitiveTypes = new Set([
 is.primitive = x => is.null(x) || primitiveTypes.has(typeof x);
 
 is.integer = Number.isInteger;
+is.safeInteger = Number.isSafeInteger;
 
 is.plainObject = x => {
 	// From: https://github.com/sindresorhus/is-plain-obj/blob/master/index.js

readme.md

@@ -128,6 +128,11 @@ is.asyncFunction(() => {});
 JavaScript primitives are as follows: `null`, `undefined`, `string`, `number`, `boolean`, `symbol`.
 
 ##### .integer(value)
+
+##### .safeInteger(value)
+
+Returns `true` if `value` is a [safe integer](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/isSafeInteger).
+
 ##### .plainObject(value)
 
 An object is plain if it's created by either `{}`, `new Object()`, or `Object.create(null)`.

test.js

@@ -98,6 +98,10 @@ const types = new Map([
 		new Object() // eslint-disable-line no-new-object
 	]],
 	['integer', 6],
+	['safeInteger', [
+		Math.pow(2, 53) - 1,
+		-Math.pow(2, 53) + 1
+	]],
 	['domElement', [
 		'div',
 		'input',
@@ -160,7 +164,7 @@ test('is.string', t => {
 });
 
 test('is.number', t => {
-	testType(t, 'number', ['nan', 'integer', 'infinite']);
+	testType(t, 'number', ['nan', 'integer', 'safeInteger', 'infinite']);
 });
 
 test('is.boolean', t => {
@@ -312,10 +316,16 @@ test('is.primitive', t => {
 });
 
 test('is.integer', t => {
-	testType(t, 'integer', ['number']);
+	testType(t, 'integer', ['number', 'safeInteger']);
 	t.false(m.integer(1.4));
 });
 
+test('is.safeInteger', t => {
+	testType(t, 'safeInteger', ['number', 'integer']);
+	t.false(m.safeInteger(Math.pow(2, 53)));
+	t.false(m.safeInteger(-Math.pow(2, 53)));
+});
+
 test('is.plainObject', t => {
 	testType(t, 'plainObject', ['object', 'promise']);
 });