src/utils.mjs: Add undefinedAsNull()

2 files changed, 22 insertions, 0 deletions

diff --git a/src/utils.mjs b/src/utils.mjs
index cde6934..30a0f1a 100644
--- a/src/utils.mjs
+++ b/src/utils.mjs
@@ -82,3 +82,5 @@ export const partial = (fn, ...startArgs) =>
 		fn(...startArgs, ...endArgs);
 
 export const strSortFn = (a, b) => a.localeCompare(b, "POSIX");
+
+export const undefinedAsNull = x => x === undefined ? null : x;
diff --git a/tests/js/utils.mjs b/tests/js/utils.mjs
index 178f6c8..d16bae8 100644
--- a/tests/js/utils.mjs
+++ b/tests/js/utils.mjs
@@ -11,6 +11,7 @@ import {
 	promisify,
 	partial,
 	strSortFn,
+	undefinedAsNull,
 } from "../../src/utils.mjs";
 
 const test_eq = t => {
@@ -361,6 +362,24 @@ const test_strSortFn = t => {
 	});
 };
 
+const test_undefinedAsNull = t => {
+	t.start("undefinedAsNull()");
+
+	t.test("null for undefined or null", () => {
+		assert.equal(undefinedAsNull(undefined), null);
+		assert.equal(undefinedAsNull(null),      null);
+	});
+
+	t.test("identity otherwise", () => {
+		const expected = [
+			" ", "", 0, 1, -1.1, true, false,
+			[], [ "" ], {}, { k: "v" },
+		];
+		const given = expected.map(undefinedAsNull);
+		assert.deepEqual(given, expected);
+	});
+};
+
 
 await runner.runTests([
 	test_eq,
@@ -372,4 +391,5 @@ await runner.runTests([
 	test_promisify,
 	test_partial,
 	test_strSortFn,
+	test_undefinedAsNull,
 ]);