add polyfill and tests for new sliding method

Author: michaelficarra

src/index.ts

@@ -57,6 +57,35 @@ function windows(this: unknown, windowSize: unknown): Generator<unknown> {
   return windowsImpl(this as Iterator<unknown>, windowSize);
 }
 
+function* slidingImpl<A>(iter: Iterator<A>, windowSize: number): Generator<Array<A>> {
+  let buffer = [];
+  for (const elem of liftIterator(iter)) {
+    if (buffer.length === windowSize) {
+      buffer.shift();
+    }
+    buffer.push(elem);
+    if (buffer.length === windowSize) {
+      yield buffer.slice();
+    }
+  }
+  if (0 < buffer.length && buffer.length < windowSize) {
+    yield buffer;
+  }
+}
+
+function sliding<A>(this: Iterator<A>, windowSize: number): Generator<Array<A>>
+function sliding(this: unknown, windowSize: unknown): Generator<unknown> {
+  if (
+    typeof windowSize !== 'number'
+    || windowSize <= 0
+    || Math.floor(windowSize) !== windowSize
+    || windowSize >= Math.pow(2, 53)
+  ) {
+    throw new RangeError;
+  }
+  return slidingImpl(this as Iterator<unknown>, windowSize);
+}
+
 Object.defineProperty(IteratorPrototype, 'chunks', {
   configurable: true,
   writable: true,
@@ -70,3 +99,10 @@ Object.defineProperty(IteratorPrototype, 'windows', {
   enumerable: false,
   value: windows,
 });
+
+Object.defineProperty(IteratorPrototype, 'sliding', {
+  configurable: true,
+  writable: true,
+  enumerable: false,
+  value: sliding,
+});

test/index.mjs

@@ -97,3 +97,45 @@ test('windows', async t => {
     nats(1).windows(Math.pow(2, 53));
   }, RangeError)
 });
+
+test('sliding', async t => {
+  assert.deepEqual(
+    Array.from(nats(5).sliding(2)),
+    [[0, 1], [1, 2], [2, 3], [3, 4]],
+  );
+  assert.deepEqual(
+    Array.from(nats(5).sliding(1)),
+    [[0], [1], [2], [3], [4]],
+  );
+  assert.deepEqual(
+    Array.from(nats(6).sliding(3)),
+    [[0, 1, 2], [1, 2, 3], [2, 3, 4], [3, 4, 5]],
+  );
+  assert.deepEqual(
+    Array.from(nats(6).sliding(100)),
+    [[0, 1, 2, 3, 4, 5]],
+  );
+  assert.deepEqual(
+    Array.from(nats(0).sliding(2)),
+    [],
+  );
+
+  assert.throws(() => {
+    nats(1).sliding()
+  }, RangeError)
+  assert.throws(() => {
+    nats(1).sliding([2]);
+  }, RangeError)
+  assert.throws(() => {
+    nats(1).sliding(0);
+  }, RangeError)
+  assert.throws(() => {
+    nats(1).sliding(-1);
+  }, RangeError)
+  assert.throws(() => {
+    nats(1).sliding(1.5);
+  }, RangeError)
+  assert.throws(() => {
+    nats(1).sliding(Math.pow(2, 53));
+  }, RangeError)
+});