Move internal modules to “internal” folder.

.internal/baseDelay.js

@@ -0,0 +1,18 @@
+/**
+ * The base implementation of `delay` and `defer` which accepts `args`
+ * to provide to `func`.
+ *
+ * @private
+ * @param {Function} func The function to delay.
+ * @param {number} wait The number of milliseconds to delay invocation.
+ * @param {Array} args The arguments to provide to `func`.
+ * @returns {number|Object} Returns the timer id or timeout object.
+ */
+function baseDelay(func, wait, args) {
+  if (typeof func != 'function') {
+    throw new TypeError('Expected a function');
+  }
+  return setTimeout(() => func(...args), wait);
+}
+
+export default baseDelay;