feat: implement fallback. close #19

src/fallback.js

@@ -0,0 +1,34 @@
+/**
+ * @license MIT
+ * @copyright (c) 2021 Julien Gonzalez <hello@spinjs.com>
+ */
+
+const {curry} = require('./functions');
+
+/**
+* @namespace
+* @alias ROOT
+*/
+module.exports = {
+  /**
+   * Returns `x` if and only if `y` is nil.
+   * Otherwise returns `y`.
+   *
+   * @example
+   * ```javascript
+   * const your_name = fallback('john doe');
+   * 
+   * your_name('tom');
+   * //=> 'tom'
+   *
+   * your_name(null);
+   * //=> 'john doe'
+   * ```
+   *
+   * @public
+   * @param {?} x Any
+   * @param {?} y Any
+   * @return {?}
+   */
+  fallback: curry((x, y) => y == null ? x : y)
+};

test/fallback.test.js

@@ -0,0 +1,12 @@
+const test = require('tape');
+const {fallback: sut} = require('..');
+
+test('fallback', t => {
+  const your_name = sut('john doe');
+  t.equal('tom', your_name('tom'));
+  t.equal(0, your_name(0));
+  t.equal(false, your_name(false));
+  t.equal('john doe', your_name(null));
+  t.equal('john doe', your_name(undefined));
+  t.end();
+});