move misc to js/ui

1-js/99-js-misc/01-proxy/02-array-negative/task.md

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+
+# Accessing array[-1]
+
+In some languages, we can access array elements using negative indexes, counted from the end.
+
+Like this:
+
+```js
+let array = [1, 2, 3];
+
+array[-1]; // 3, the last element
+array[-2]; // 2, one step from the end
+array[-3]; // 1, two steps from the end
+```
+
+In other words, `array[-N]` is the same as `array[array.length - N]`.
+
+Create a proxy to implement that behavior.
+
+That's how it should work:
+
+```js
+let array = [1, 2, 3];
+
+array = new Proxy(array, {
+  /* your code */
+});
+
+alert( array[-1] ); // 3
+alert( array[-2] ); // 2
+
+// Other array functionality should be kept "as is"
+```