feat(issymbol): adding new util for checking if a value is a symbol

src/getTag.ts

@@ -1,5 +1,3 @@
-const toString = Object.prototype.toString;
-
 /**
  * Gets the `toStringTag` of `value`.
  * @private
@@ -15,7 +13,5 @@ const toString = Object.prototype.toString;
  * ```
  */
 export function getTag(value: any): string {
-  return toString.call(value);
+  return Object.prototype.toString.call(value);
 }
-
-export default getTag;

src/isSymbol.test.ts

@@ -0,0 +1,24 @@
+import { isSymbol } from './isSymbol';
+
+describe('isSymbol', () => {
+  it('should return `true` for symbols', () => {
+    expect(isSymbol(Symbol())).toEqual(true);
+    expect(isSymbol(Object(Symbol()))).toEqual(true);
+  });
+
+  it('should return `false` for non-symbols', () => {
+    expect(isSymbol()).toEqual(false);
+    expect(isSymbol(null)).toEqual(false);
+    expect(isSymbol(undefined)).toEqual(false);
+    expect(isSymbol(false)).toEqual(false);
+    expect(isSymbol(0)).toEqual(false);
+    expect(isSymbol(NaN)).toEqual(false);
+    expect(isSymbol('')).toEqual(false);
+    expect(isSymbol([1, 2, 3])).toEqual(false);
+    expect(isSymbol(new Date())).toEqual(false);
+    expect(isSymbol(new Error())).toEqual(false);
+    expect(isSymbol(Array.prototype.slice)).toEqual(false);
+    expect(isSymbol({ '0': 1, length: 1 })).toEqual(false);
+    expect(isSymbol(/x/)).toEqual(false);
+  });
+});

src/isSymbol.ts

@@ -0,0 +1,24 @@
+import { getTag } from './getTag';
+
+/**
+ * Checks if `value` is classified as a `Symbol` primitive or object.
+ *
+ * @since 3.0.5
+ * @category Lang
+ * @param {*} value The value to check.
+ * @returns {boolean} Returns `true` if `value` is a symbol, else `false`.
+ * @example
+ *
+ * isSymbol(Symbol.iterator)
+ * // => true
+ *
+ * isSymbol('abc')
+ * // => false
+ */
+export function isSymbol(value?: any): boolean {
+  const type = typeof value;
+  return (
+    type === 'symbol' ||
+    (type === 'object' && value !== null && getTag(value) === '[object Symbol]')
+  );
+}