fix(diff): print BigInts within JSON correctly (#186)

* Detect BigInt within circular() and properly convert them within stringify

* narrower bigint check

* update test expectants

* fix: avoid bigint syntax errors in Node8

Co-authored-by: Luke Edwards <luke.edwards05@gmail.com>

Author: rdmurphy

src/diff.js

@@ -181,6 +181,7 @@ export function circular() {
 	return function print(key, val) {
 		if (val === void 0) return '[__VOID__]';
 		if (typeof val === 'number' && val !== val) return '[__NAN__]';
+		if (typeof val === 'bigint') return val.toString();
 		if (!val || typeof val !== 'object') return val;
 		if (cache.has(val)) return '[Circular]';
 		cache.add(val); return val;

test/diff.js

@@ -2,6 +2,7 @@ import { suite } from 'uvu';
 import * as assert from 'uvu/assert';
 import * as $ from '../src/diff';
 
+const isNode8 = process.versions.node.startsWith('8.');
 const strip = str => str.replace(/[\u001B\u009B][[\]()#;?]*(?:(?:(?:[a-zA-Z\d]*(?:;[-a-zA-Z\d\/#&.:=?%@~_]*)*)?\u0007)|(?:(?:\d{1,4}(?:;\d{0,4})*)?[\dA-PR-TZcf-ntqry=><~]))/g, '');
 
 const arrays = suite('arrays');
@@ -1167,4 +1168,17 @@ stringify('should retain `undefined` and `NaN` values :: Array', () => {
 	);
 });
 
+if (!isNode8) {
+	// Not currently supporting :: Object(BigInt(3)) && Object(4n)
+	stringify('should handle `BigInt` values correctly', () => {
+		let bigint = eval('100n'); // avoid Node8 syntax error
+		assert.is($.stringify(BigInt(1)), '"1"');
+		assert.is($.stringify(bigint), '"100"');
+		assert.is(
+			$.stringify([BigInt(1), bigint]),
+			'[\n  "1",\n  "100"\n]'
+		);
+	});
+}
+
 stringify.run();