Update: Allow first() to accept a single-item array (fixes #26)

src/env.js

@@ -105,11 +105,12 @@ export class Env {
      * @param {string} [defaultValue] The default value to return if the
      *      environment variable is not found.
      * @returns {string|undefined} The environment variable value if found or undefined if not.
+     * @throws {TypeError} If keys is not an array with at least one item.
      */
     first(keys, defaultValue) {
 
-        if (!Array.isArray(keys) || keys.length < 2) {
-            throw new TypeError("First argument must be an array of two or more strings.");
+        if (!Array.isArray(keys) || keys.length < 1) {
+            throw new TypeError("First argument must be an array of one or more strings.");
         }
 
         for (const key of keys) {

tests/env.test.js

@@ -92,16 +92,22 @@ describe("Env", () => {
 
         });
 
-        it("should throw an error when the first argument doesn't have at least two items", () => {
+        it("should throw an error when the first argument doesn't have at least one item", () => {
             const env = new Env(source);
 
             assert.throws(() => {
-                env.first(["USERNAME"]);
+                env.first([]);
             }, /First argument/);
 
         });
 
-        it("should get the first environment variable when it exists", () => {
+        it("should get the first environment variable when one exists", () => {
+            const env = new Env(source);
+            const value = env.first(["USERNAME"]);
+            assert.strictEqual(value, source.USERNAME);
+        });
+
+        it("should get the first environment variable when only one exists", () => {
             const env = new Env(source);
             const value = env.first(["USERNAME", "ALT_USERNAME"]);
             assert.strictEqual(value, source.USERNAME);