fix: yield first mapped/filtered values

packages/it-filter/src/index.ts

@@ -49,7 +49,11 @@ function filter <T> (source: Iterable<T> | AsyncIterable<T>, fn: (val: T) => boo
   const func = fn as (val: T) => boolean
 
   return (function * () {
-    for (const entry of source) {
+    if (res === true) {
+      yield value
+    }
+
+    for (const entry of peekable) {
       if (func(entry)) {
         yield entry
       }

packages/it-filter/test/index.spec.ts

@@ -18,6 +18,13 @@ describe('it-filter', () => {
     expect(res).to.deep.equal([3, 4])
   })
 
+  it('should filter all values less than 2', async () => {
+    const res = all(filter(values(), val => val < 2))
+
+    expect(res[Symbol.iterator]).to.be.ok()
+    expect(res).to.deep.equal([0, 1])
+  })
+
   it('should filter all values greater than 2 with a promise', () => {
     const res = all(filter(values(), val => val > 2))
 

packages/it-foreach/src/index.ts

@@ -44,7 +44,9 @@ function forEach <T> (source: Iterable<T> | AsyncIterable<T>, fn: (thing: T) =>
   const func = fn as (val: T) => void
 
   return (function * () {
-    for (const val of source) {
+    yield value
+
+    for (const val of peekable) {
       func(val)
       yield val
     }

packages/it-map/package.json

@@ -135,7 +135,8 @@
     "release": "aegir release"
   },
   "devDependencies": {
-    "aegir": "^38.1.7"
+    "aegir": "^38.1.7",
+    "it-all": "^3.0.0"
   },
   "dependencies": {
     "it-peekable": "^3.0.0"

packages/it-map/src/index.ts

@@ -44,7 +44,9 @@ function map <I, O> (source: AsyncIterable<I> | Iterable<I>, func: (val: I) => O
   const fn = func as (val: I) => O
 
   return (function * () {
-    for (const val of source) {
+    yield res as O
+
+    for (const val of peekable) {
       yield fn(val)
     }
   })()

packages/it-map/test/index.spec.ts

@@ -1,5 +1,6 @@
 import { expect } from 'aegir/chai'
 import map from '../src/index.js'
+import all from 'it-all'
 
 async function * asyncGenerator (): AsyncGenerator<number> {
   yield 1
@@ -18,44 +19,44 @@ describe('it-map', () => {
     const gen = map(asyncGenerator(), (val) => val + 1)
     expect(gen[Symbol.asyncIterator]).to.be.ok()
 
-    for await (const result of gen) {
-      expect(result).to.equal(2)
-    }
+    const results = await all(gen)
+    expect(results).to.have.lengthOf(1)
+    expect(results).to.have.nested.property('[0]', 2)
   })
 
   it('should map an async iterator to a promise', async () => {
     const gen = map(asyncGenerator(), async (val) => val + 1)
     expect(gen[Symbol.asyncIterator]).to.be.ok()
 
-    for await (const result of gen) {
-      expect(result).to.equal(2)
-    }
+    const results = await all(gen)
+    expect(results).to.have.lengthOf(1)
+    expect(results).to.have.nested.property('[0]', 2)
   })
 
   it('should map an iterator', () => {
     const gen = map(generator(), (val) => val + 1)
     expect(gen[Symbol.iterator]).to.be.ok()
 
-    for (const result of gen) {
-      expect(result).to.equal(2)
-    }
+    const results = all(gen)
+    expect(results).to.have.lengthOf(1)
+    expect(results).to.have.nested.property('[0]', 2)
   })
 
   it('should map an iterator to a promise', async () => {
     const gen = map(generator(), async (val) => val + 1)
     expect(gen[Symbol.asyncIterator]).to.be.ok()
 
-    for await (const result of gen) {
-      expect(result).to.equal(2)
-    }
+    const results = await all(gen)
+    expect(results).to.have.lengthOf(1)
+    expect(results).to.have.nested.property('[0]', 2)
   })
 
   it('should map a source', async () => {
     const gen = map(source(), (val) => val + 1)
     expect(gen[Symbol.asyncIterator]).to.be.ok()
 
-    for await (const result of gen) {
-      expect(result).to.equal(2)
-    }
+    const results = await all(gen)
+    expect(results).to.have.lengthOf(1)
+    expect(results).to.have.nested.property('[0]', 2)
   })
 })