👍 Add isSymbol

Author: lambdalisue

is.ts

@@ -205,6 +205,13 @@ export function isNullish(x: unknown): x is null | undefined {
   return x == null;
 }
 
+/**
+ * Return `true` if the type of `x` is `symbol`.
+ */
+export function isSymbol(x: unknown): x is symbol {
+  return typeof x === "symbol";
+}
+
 export type OneOf<T> = T extends (infer U)[]
   ? T extends Predicate<infer U>[] ? U : T
   : T;
@@ -245,5 +252,6 @@ export default {
   Null: isNull,
   Undefined: isUndefined,
   Nullish: isNullish,
+  Symbol: isSymbol,
   OneOf: isOneOf,
 };

is_test.ts

@@ -17,6 +17,7 @@ import is, {
   isRecord,
   isRecordOf,
   isString,
+  isSymbol,
   isTupleOf,
   isUndefined,
   Predicate,
@@ -32,6 +33,7 @@ const examples = {
   function: [function () {}],
   null: [null],
   undefined: [undefined],
+  symbol: [Symbol("a"), Symbol("b"), Symbol("c")],
 };
 
 function stringify(x: unknown): string {
@@ -240,6 +242,10 @@ Deno.test("isNullish", async (t) => {
   await testWithExamples(t, isNullish, ["null", "undefined"]);
 });
 
+Deno.test("isSymbol", async (t) => {
+  await testWithExamples(t, isSymbol, ["symbol"]);
+});
+
 Deno.test("isOneOf<T>", async (t) => {
   await t.step("returns proper type predicate", () => {
     const preds = [isNumber, isString, isBoolean];