feat: reduce functions

src/functions/reduce.spec.ts

@@ -0,0 +1,23 @@
+import {reduceTruthy, reduceFalsy} from '../index'
+
+describe('Reduce Functions', () => {
+  it('should reduce truthy', () => {
+    expect(reduceTruthy([true, true, false, true], e => e)).toBeFalsy()
+    expect(reduceTruthy([true, true, true, true], e => e)).toBeTruthy()
+    expect(reduceTruthy([false, true, true, true], e => e)).toBeFalsy()
+  })
+
+  it('should only call the check function until it hits a false', () => {
+    const check = jest.fn(e => e)
+
+    reduceTruthy([true, true, false, true, true, true, false, true], check)
+
+    expect(check).toHaveBeenCalledTimes(3)
+  })
+
+  it('should reuce falsey', () => {
+    expect(reduceFalsy([false, false, true, false], e => e)).toBeFalsy()
+    expect(reduceFalsy([false, false, false, false], e => e)).toBeTruthy()
+    expect(reduceFalsy([true, false, true, false], e => e)).toBeFalsy()
+  })
+})

src/functions/reduce.ts

@@ -0,0 +1,29 @@
+/**
+ * Reduce the array into a single boolean value for if the check function returns true.
+ *
+ * _once the first `false` is encountered `check` is not run again_
+ *
+ * @param array The array to test
+ * @param check The function to check the array entries with
+ * @returns `true` if `check` only ever returned `true`, otherwise `false`
+ */
+export const reduceTruthy = <T>(array: T[], check: (entry: T) => boolean) => {
+  return array.reduce((result, entry) => {
+    if (!result) return false
+
+    return check(entry)
+  }, true)
+}
+
+/**
+ * Reduce the array into a single boolean value for if the check function returns false.
+ *
+ * _once the first `true` is encountered `check` is not run again_
+ *
+ * @param array The array to test
+ * @param check The function to check the array entries with
+ * @returns `true` if `check` only ever returned `false`, otherwise `false`
+ */
+export const reduceFalsy = <T>(array: T[], check: (entry: T) => boolean) => {
+  return reduceTruthy(array, e => !check(e))
+}

src/index.ts

@@ -33,6 +33,7 @@ export {indexedBy, IndexedArray, IndexedByOptions} from './functions/indexed-by'
 export {keys} from './functions/keys'
 export {mapProperty} from './functions/map-property'
 export {rangeAsString, rangeAsArray} from './functions/range-as-string'
+export {reduceTruthy, reduceFalsy} from './functions/reduce'
 export {propIs, propIsNot} from './functions/selectors'
 export {nl2br} from './functions/nl2br'
 export {parameterize} from './functions/parameterize'