Add interval

.eslintrc.json

@@ -14,6 +14,7 @@
         "ecmaVersion": 12
     },
     "rules": {
-        "unicorn/no-null": "off"
+        "unicorn/no-null": "off",
+        "sonarjs/prefer-while": "off"
     }
 }

TODO.md

@@ -1,6 +1,7 @@
 # Today
 - rename: create-number-generator -> create-async-number-generator
 - eslint
+- speed up tests
 
 # Someday
 - Add toBeNear Jest matcher

src/interval/index.js

@@ -0,0 +1,24 @@
+const sleep = require('../sleep')
+
+async function* interval(ms, gen) {
+  for await (let value of gen) {
+    yield value
+    await sleep(ms)
+  }
+}
+
+function composable(ms) {
+  return async function* composableInterval(gen) {
+    yield* interval(ms, gen)
+  }
+}
+
+function main(ms, gen) {
+  if (!gen) {
+    return composable(ms)
+  } else {
+    return interval(ms, gen)
+  }
+}
+
+module.exports = main

src/interval/test.js

@@ -0,0 +1,23 @@
+const interval = require('.')
+const take = require('../take')
+const consume = require('../consume')
+const compose = require('../compose')
+const createFibonacciGenerator = require('../_shared/create-fibonacci-generator')
+
+it('consumes generator every `ms` miliseconds', async () => {
+  const composed = take(4, interval(10, createFibonacciGenerator()))
+  const past = Date.now()
+  const output = await consume(composed)
+
+  expect(output).toEqual([1, 1, 2, 3])
+  expect(Date.now() - past).toBeGreaterThanOrEqual(40)
+})
+
+it('is composable', async () => {
+  const composed = compose(createFibonacciGenerator(), interval(10), take(4))
+  const past = Date.now()
+  const output = await consume(composed)
+
+  expect(output).toEqual([1, 1, 2, 3])
+  expect(Date.now() - past).toBeGreaterThanOrEqual(40)
+})