Create a JavaScript util `castArray`

- Allows easy conversion of any value/s supplied into an array or keep as an array if it's already one

client/src/utils/castArray.test.js

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+import { castArray } from './castArray';
+
+describe('castArray', () => {
+  it('should return an empty array by default', () => {
+    expect(castArray()).toEqual([]);
+  });
+
+  it('should the provided argument wrapped as an array if it is not one', () => {
+    expect(castArray(null)).toEqual([null]);
+    expect(castArray(undefined)).toEqual([undefined]);
+    expect(castArray(3)).toEqual([3]);
+  });
+
+  it('should return the provided argument as an array if it is one', () => {
+    expect(castArray([])).toEqual([]);
+    expect(castArray([1, 2, 3])).toEqual([1, 2, 3]);
+    expect(castArray([1, 2, ['nested', 'true']])).toEqual([
+      1,
+      2,
+      ['nested', 'true'],
+    ]);
+  });
+
+  it('should return a set of arguments as an array', () => {
+    expect(castArray(1, 2, 3)).toEqual([1, 2, 3]);
+    expect(castArray(null, undefined)).toEqual([null, undefined]);
+  });
+});

client/src/utils/castArray.ts

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+/**
+ * Converts the provided args or single argument to an array.
+ * Even if not originally supplied as one.
+ */
+export const castArray = (...args) => args.flat(1);